Methods and systems for wireless networks with relays

ABSTRACT

Methods and systems are provided for use with wireless networks having one or more cell in which each cell includes a base station (BS), at least one relay station (RS) and at least one mobile station (MS). The at least one relay station can be used as an intermediate station for providing communication between the BS and MS. Methods are provided for an RS to initially access the network, access of the RS by MSs initially accessing the network, methods of allocating OFDM resources for communicating between the BS, RS and/or MS for example dividing transmission resources into uplink and downlink transmissions, and methods of inserting pilot symbols into transmission resources used by the RS. In some embodiments on the invention, the methods are consistent and/or can be used in conjunction with existing standards such as 802.16e.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/093,202 filed on May 9, 2008, which claims the benefit of and is aNational Phase Entry of International Application No. PCT/CA2006/00185filed on Nov. 10, 2006, and claims the benefit of U.S. ProvisionalPatent Application No. 60/735,940 filed on Nov. 10, 2005, U.S.Provisional Patent Application No. 60/809,341 filed on May 31, 2006,U.S. Provisional Patent Application No. 60/822,816 filed on Aug. 18,2006 and U.S. Provisional Patent Application No. 60/822,960 filed onAug. 21, 2006, which are all hereby incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The invention relates to the field of wireless communications, morespecifically to systems and methods for supporting Orthogonal FrequencyDivision Multiplexed (OFDM) communication using relays.

BACKGROUND OF THE INVENTION

Orthogonal frequency division multiplexing (OFDM) is a form ofmultiplexing that distributes data over a number of carriers that have avery precise spacing in the frequency domain. The precise spacing of thecarriers provides several benefits such as high spectral efficiency,resiliency to radio frequency interference and lower multi-pathdistortion. Due to its beneficial properties and superior performance inmulti-path fading wireless channels, OFDM has been identified as auseful technique in the area of high data-rate wireless communication,for example wireless metropolitan area networks (MAN). Wireless MAN arenetworks to be implemented over an air interface for fixed, portable,and mobile broadband access systems.

In some wireless networks, a mobile station (MS) in a given cell is onlyserved by its serving base station (BS).

One drawback of such wireless networks is that MSs near an edge of thegiven cell suffer performance loss due to interference from other cellsin cellular networks and propagation loss in non-cellular networks whichresults in limited data rates and gaps in coverage of the given cell.

While soft hand off can be used in cellular networks to improveperformance to some extent for MSs at the cell edge, the improvedperformance comes at the cost of additional system complexity and aspectrum efficiency penalty.

One way to improve the performance is to introduce a fixed relay station(RS) into wireless networks. The use of an RS may provide a) enhancedsystem capacity, b) enhanced data rate and cell coverage, c) reduced MStransmit power requirements and d) allow less expensive poweramplification.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a methodcomprising: allocating an OFDM transmission resource having a frequencydimension consisting of a set of OFDM sub-carriers and a time dimensionconsisting of OFDM symbols using zones, each zone comprising a set ofconsecutive OFDM symbols by: for a base station (BS), allocating a DL_MSzone for transmitting to mobile stations (MSs), and allocating a DL_RSzone for transmitting to relay stations (RSs); for each relay station,allocating a DL_MS zone for transmitting to mobile stations, andallocating a DL_RS zone for transmitting to other relay stations ifpresent; for the base station, allocating a UL_MS zone for receivingfrom mobile stations, and allocating a UL_RS zone for receiving fromrelay stations; for each relay station, allocating a UL_MS zone forreceiving from mobile stations, and allocating a UL_RS zone forreceiving from other relay stations if present.

In some embodiments, all of the zones are on a single OFDM carrier.

In some embodiments, the method further comprises separating uplinktransmission from downlink transmissions using TDD (time divisionduplexing).

In some embodiments, allocating comprises defining TDD frames, each TDDframe comprising a DL sub-frame during which downlink transmissions forthe BS and RSs takes place, and a UL sub-frame during which uplinktransmissions to the BS and RSs takes place, the DL sub-frame and the ULsub-frame being sequentially transmitted.

In some embodiments, the method further comprises separating uplinktransmission from downlink transmissions using FDD (frequency divisionduplexing).

In some embodiments, allocating comprises defining FDD frames, each FDDframe comprising a DL frame during which downlink transmissions for theBS and RSs takes place, and a UL frame during which uplink transmissionsto the BS and RSs takes place, the DL frame and the UL frame beingsimultaneously transmitted using a different frequency resource.

In some embodiments, the method comprises: using an entire OFDM band ofa single carrier for communications between BS and RS, communicationsbetween RS and RS, communications between BS and MS links, andcommunications between RS and MS, with no resource reuse among the BSand different tier RS.

In some embodiments, the method further comprises allocating in a mannerthat employs resource reuse among RSs that are the same number of hopsfrom the BS.

In some embodiments, the method comprises: using an entire OFDM band ofa single carrier for communications between BS and RS, communicationsbetween RS and RS, communications between BS and MS links, andcommunications between RS and MS, and allocating in a manner employingresource reuse among the BS and different tier RS.

In some embodiments, the method further comprises allocating in a manneremploying resource reuse among RSs that are the same number of hops fromthe BS.

In some embodiments, the method comprises: using an entire OFDM band forsome communications types, and using a partial OFDM band for somecommunications types with no reuse among BS and different tier RS, thecommunications types comprising BS to and/or from RS, RS to and/or fromRS, BS to and/or from MS, RS to and/or from MS.

In some embodiments, using an entire OFDM band for some communicationstypes comprises: using an entire OFDM band for communications between RSand RS and for communications between RS and BS.

In some embodiments, using a partial OFDM band for some communicationstypes comprises: using a partial OFDM band for communications between MSand RS and for communications between MS to BS.

In some embodiments, using a partial OFDM band for communicationsbetween MS and RS and for communications between MS to BS comprises:using a respective partial OFDM band for BS transmissions to MSs and foreach tier of RS transmissions to MSs; using a respective partial OFDMband for the BS receptions from MSs and for and each tier of RSreceptions from MSs.

In some embodiments, the method further comprises allocating in a manneremploying resource reuse among RSs that are the same number of hops fromthe BS.

In some embodiments, the method comprises: using a first OFDM band forsome communications types, and using parts of a second OFDM band forsome communication types, the communications types comprising BS toand/or from RS, RS to and/or from RS, BS to and/or from MS, RS to and/orfrom MS.

In some embodiments, the method comprises: using a first OFDM band forsome communications types, a second OFDM band for some communicationstypes, and using parts of a third OFDM band for some communicationstypes, the communications types comprising BS to and/or from RS, RS toand/or from RS, BS to and/or from MS, RS to and/or from MS.

In some embodiments, using a first OFDM band for some communicationscomprises using the first OFDM band for communications between RS andBS; using a second OFDM band for some communications types comprisesusing the second OFDM band for communications between RS and RS; usingparts of a third OFDM band for some communications types comprises usinga respective partial OFDM band for the BS and each tier of RStransmissions to MSs, and using a respective partial OFDM band for theBS and each tier of RS receptions from MSs.

In some embodiments, the method comprises: each relay stationtransmitting a first preamble for use by mobile stations; each relaystation transmitting a second preamble for use by other relay stations.

In some embodiments, the first preamble is an 802.16e preamble.

In some embodiments, the second preamble is transmitted by each RS oncein every N frames, where N>=1.

In some embodiments, the second preamble has a structure consistent with802.16e.

In some embodiments, the second preamble is transmitted within a ULsub-frame for TDD implementations or a UL frame for FDD implementations.

In some embodiments, the RSs transmission and receiving of the secondpreamble is synchronized so that at each second preamble transmissiontime, only one RS per tier is receiving and all others are transmitting.

According to an aspect of the invention, there is provided a method ofchannel coordination for RSs, a channel comprising an OFDM zone, themethod comprising: each RS measuring neighboring station's signalstrength and/or channel quality and reporting this to a BS; each RSreporting its capability to the BS; the BS determining a channelassignment for each RS and broadcasting this information to the RSs.

According to an aspect of the invention, there is provided a method ofchannel coordination for RSs, a channel comprising an OFDM zone, themethod comprising: each one hop RS measuring neighboring station'ssignal strength and/or channel quality and reporting this to a BS; eachone hop RS reporting its capability to the BS; the BS determining achannel assignment for each one hop RS and broadcasting this informationto the RSs; each one hop RS determining channel assignment for next hopRSs and so on.

According to an aspect of the invention, there is provided a method ofchannel coordination for RSs, a channel comprising an OFDM zone, themethod comprising: each RS in any of a first N hops from a BS measuringneighboring station's signal strength and/or channel quality andreporting this to the BS; each RS in any of the first N hops reportingits capability to the BS; the BS determining a channel assignment foreach RS in any of the first N hops and broadcasting this information tothe involved RSs; each RS in hops subsequent to the Nth hop determiningchannel assignment for each next hop RSs.

According to an aspect of the invention, there is provided a method ofallocating RS DL Resource comprising: allocating a persistent resourcefor RS DL communications for a period of time longer than a frame,wherein a frame comprises multiple OFDM symbols.

In some embodiments, the method further comprises: updating thepersistent resource allocation from time to time; supplementing thepersistent resource allocation from time to time; terminating thepersistent resource allocation when appropriate.

In some embodiments, updating the persistent resource allocationcomprises updating any one or more of: resource size information;resource location information; and modulation code scheme (MCS)information that at least in part defines the persistent resourceallocation.

According to an aspect of the invention, there is provided a method ofperforming RS UL Resource Allocation comprising: in a non-contentionbased approach, allocating each RS a dedicated UL resource for the RS tosend a resource request MAC (media access control) header every Nframes, where N is a pre-defined number and using the dedicated resourceto send request UL resources; the BS responding with a resource grant.

In some embodiments, sending the resource request MAC header comprisessending the following fields: request type, Bandwidth request, and HCS(header check sequence).

According to an aspect of the invention, there is provided a method ofperforming RS UL Resource Allocation comprising: in a contention basedapproach, the RS sending a BW (bandwidth) request ranging message torequest a UL resource; the BS responding with a resource grant.

In some embodiments, sending a BW request ranging message comprisessending the following fields: request type, Bandwidth request, stationID and HCS.

In some embodiments, the resource allocation is a persistent UL resourceallocation, the method further comprising: updating the persistent ULresource allocation from time to time; supplementing the persistent ULresource allocation from time to time; terminating the persistent ULresource allocation when appropriate.

According to an aspect of the invention, there is provided a method ofperforming MS UL Resource Allocation comprising: disabling a piggybacksub-header function for a multi-hop-away MS; a MS using a BW requestheader along with data if there is a UL resource available.

According to an aspect of the invention, there is provided a method ofperforming MS UL Resource Allocation comprising: an RS associated with aMS forwarding a piggyback sub-header to a BS; the BS decrypting thepiggyback sub-header and informing the RS associated with the MS.

According to an aspect of the invention, there is provided a method offacilitating intra-cell peer-to-peer communication comprising:maintaining a destination address table for a BS that includesdestination addresses that are served by the BS; upon receiving a packetcontaining a destination address, determining if the destination addressis in the address table or not; if the destination address is within thetable, routing the packet towards the destination without upper layerprocessing, and otherwise routing the packet for upper layer processing.

In some embodiments, routing the packet for upper layer processingcomprises: performing DL classification and CID (connectionidentification) mapping and sending the packet to a destination MS or RSassociated with the destination MS.

In some embodiments, the method further comprises updating the tableupon at least one of the following occurrences: after a MS enters anetwork; at a MS hand off when the MS leaves a cell served by a givenBS; and at a MS hand off when the MS enters a cell served by a given BS.

According to an aspect of the invention, there is provided a method foruse in an OFDM communication system employing relay stations comprising:dividing communications into frames each comprising multiple OFDMsymbols; dividing the frames into first and second groups of frames, thefirst group of frames being used for communication between a basestation (BS) and RSs one-hop away from the BS, and for communicationsbetween the BS and its respective mobile stations (MSs), the first groupalso being used for communication between RSs two-hops away from the BSand its respective MSs, and the second group of frames being used forcommunication between the RSs one-hop away from the BS and any RS/MS itis communicating with.

In some embodiments, dividing the frames comprises dividing the framessuch that the first group is odd frames and the second group is evenframes.

In some embodiments, the method further comprises: the BS communicatingwith mobile stations during the second group of frames at a reducedtransmission power with respect to the transmission power used fortransmitting to the RSs.

In some embodiments, the method further comprises, after entry into anetwork, each relay station transmitting a preamble and frame controlheader (FCH) on every frame.

In some embodiments, the method further comprises: defining DL RS_Zonesfor downlink transmission from a base station or an RS to another RS andUL RS_Zones for uplink transmission from an RS to another RS, or from anRS to BS, with remaining resources available for communication with MSs.

In some embodiments, defining DL RS_Zones comprises defining a zone sizeand starting OFDM symbol within the frame according to one of: a fixedsize; a size that is slowly changed through a management media accesscontrol (MAC) message; a size that is dynamically changed and forecastby BS and DL transmitting RSs subsequent to the change.

In some embodiments, the method further comprises transmitting RSmultiplexing access profile (RS-MAP) information to indicate theresource assignments for the DL RS_zone and/or the UL RS_zone.

In some embodiments, transmitting the RS-MAP includes transmitting oneor more of: resource location information, resource size information,and modulation and coding scheme (MCS) information.

In some embodiments, the location information is a fixed offset relativeto the beginning of a frame or a fixed offset relative to RS_Zone.

In some embodiments, the modulation and code information is provided byat least one of: slowly updating the MCS information based on worst linkbudgets among all attached RS; and multicasting the MCS information tothe corresponding RSs when needed.

In some embodiments, transmitting multiple RS-MAP, each RS-MAP for arespective one RS or multiple RSs with similar channel qualities.

According to an aspect of the invention, there is provided a method foruse in an OFDM communication system employing relay stations (RSs)comprising: assigning a distinct pseudo-random noise (PN) sequence toeach base station (BS) and each respective RS.

In some embodiments, assigning the distinct PN sequence to each relaystation comprises including assigned PN index, DL_PermBase, and PRBS_IDfields in REG-REQ/RSP (registration request/response) messages.

In some embodiments, the method further comprises for purposes ofrouting, identifying each BS or RS by a BS identification (BS ID) in aMAC management message.

In some embodiments, identifying each RS comprises assigning each RS aBS ID in a REG-REQ/RSP message.

In some embodiments, assigning a distinct PN sequence for a mobilerelation station (MRS) is statically defined even when there is ahandoff.

In some embodiments, the method further comprises defining for mobilerelay stations a system reserved sub-set of PN indexes so as to avoidcollisions when a MRS moves across the network.

In some embodiments, the PN index is re-assigned during a handoff, andfurther comprising informing any attached MSs of the change and/orperforming re-synchronization.

In some embodiments, the method further comprises: performingsub-channelization using bins, wherein each bin is a band ofsub-carriers in an OFDM symbol.

In some embodiments, performing sub-channelization using bins isperformed in a manner consistent with 802.16e AMC sub-channelization.

In some embodiments, a bin is defined as a band of contiguoussub-carriers (G) in one OFDM symbol, with each bin including at leastone pilot sub-carrier.

In some embodiments, the at least one pilot sub-carrier is: for oneantenna located in the bin at a sub-carrier indexed with floor(G/2); fortwo antennas located in the bin at a first sub-carriers indexed withfloor(G/2) for a first antenna and a second sub-carrier indexed withfloor(G/2)+1 for a second antenna; and for four antennas located in thebin at a first sub-carrier indexed with floor(G/2) for a first antenna,a second sub-carrier indexed with floor(G/2)−1 for a second antenna, athird sub-carrier indexed with floor(G/2)+1 for a third antenna and afourth sub-carrier indexed with floor(G/2)+2 for a fourth antenna.

In some embodiments, performing sub-channelization comprises formingsub-channels from contiguous sets of one or more bins over one or moreconsecutive OFDM symbols.

In some embodiments, the method further comprises performing DL resourcemultiplexing between BS and RS, between RS and RS, between BS and MS andbetween RS and MS on an FDM (frequency division multiplexing) basis.

In some embodiments, the method further comprises for all availablesub-carriers used for pilot and data in an OFDM symbol; dividing thesub-carriers into a set of major groups; and dedicating a number of themajor groups of the set of major groups to BS and RS transmission and RSand RS transmission.

In some embodiments, dividing the sub-carriers into a set of majorgroups and dedicating a number of the major groups is done in a mannerconsistent with 802.16e.

In some embodiments, a sub-channel is defined so as to enlargesub-channel size, each sub-channel defined to consist of a set ofclusters that are not contiguous.

In some embodiments, the method further comprises performing UL resourcemultiplexing between RS and BS, between RS and RS, between MS and BS andbetween MS and RS using the UL RS_Zones.

In some embodiments, the method further comprises: performingsub-channelization using bins, wherein each bin is a band ofsub-carriers in an OFDM symbol.

In some embodiments, a first bin definition includes pilot symbols, anda second bin definition does not include pilot symbols, and acombination of the two bin definitions is used for a given sub-channel.

In some embodiments, the method further comprises: initially assuming anentire frame resource is initially available for use for RS relatedtransmission (DL/UL); defining RS sub-channels; assigning resources forMSs first; then assigning resources for RSs with RS sub-channels;resources assigned to RS that are already occupied by MSs are puncturedout from the assigned resource for RS.

According to an aspect of the invention, there is provided a methodcomprising: measuring strengths of a plurality of preambles in use in anOFDM network; selecting a preamble to transmit based on the measuredstrengths of the preambles.

In some embodiments, measuring strengths of a plurality of preambles inuse in the system is performed during initial network entry.

In some embodiments, selecting a preamble to transmit based on themeasured strengths of the preambles comprises: selecting at least onepreamble having a signal strength below a threshold.

In some embodiments, the method further comprises: signalling theselection of the at least one preamble back to a serving base station.

According to an aspect of the invention, there is provided a methodcomprising: a relay station measuring strengths of a plurality ofpreambles in use in an OFDM system and feeding at least some of thesemeasurements back to a serving base station; the serving base stationselecting a preamble for the relay to transmit based on the measuredstrengths of the preambles and signalling a selected preamble back tothe relay.

In some embodiments, signalling to identify preambles is performed usingpreamble indexes.

In some embodiments, feeding at least some of these measurements back toa serving base station comprises: feeding back a list that includes allthe preamble indexes whose strength measured by the RS are higher and/orlower than a pre-defined threshold.

According to an aspect of the invention, there is provided a methodcomprising: receiving strength measurement information from a mobilestation in respect of a plurality of preambles transmitted by respectiverelay stations in an OFDM network; allocating resources in a mannerresulting in resource re-use based on the strength measurements.

In some embodiments, allocating resources in a manner resulting inresource re-use based on the strength measurements comprises allocatingresources at a first relay station to the mobile station that are alsobeing allocated at a second relay station whose preamble signal strengthmeasurement was below a defined threshold.

In some embodiments, allocating resources in a manner resulting inresource re-use based on the strength measurements comprises: if a firstmobile station reports a good signal strength from a first relay stationand poor signal strength from a second relay station, and a secondmobile station reports a good signal strength from the second relaystation and poor signal strength from the first relay station, then inat least some instances assigning the same or at least partiallyoverlapping resources at the first and second relay stations fortransmitting to the first and second mobile stations with theunderstanding that this will not result in interference.

According to an aspect of the invention, there is provided a method forinitial access of a relay station (RS) into an OFDM system comprising abase station (BS) and at least one mobile station (MS), the methodcomprising: the RS performing downlink (DL) synchronization, includingframe synchronization and timing/frequency synchronization; the RSperforming cell identification and selection; the RS obtaining systemparameters from information sent on a broadcast channel by the BS to allreceiving stations and decoding the received system parameters; the RStransmitting an initial ranging code; the RS receiving a response to itstransmitted initial ranging code from the BS.

In some embodiments, the method further comprises: selecting the initialranging code from a first sub-set of ranging codes allocated for use byrelay stations in a cell serving the BS, which are different than asecond sub-set of ranging codes allocated for use by mobile stations inthe cell serving the BS.

In some embodiments, the method further comprises: selecting the initialranging code from a set of ranging codes allocated for use by relaystations and mobile stations in the cell serving the BS.

In some embodiments, the method further comprises: selecting the initialranging code from a set of ranging codes allocated for use by relaystations and transmitting the selected initial ranging code in atime-frequency region that is different than a time-frequency regionused for MS initial ranging.

According to an aspect of the invention, there is provided a method forinitial access of a relay station (RS) by a mobile station (MS) in anOFDM system comprising a base station (BS) and at least one RS, themethod comprising: the RS transmitting a common Sync symbol and preambleto enable downlink (DL) synchronization by the mobile; the RStransmitting information on a broadcast channel available to be receivedand decoded by all who receive the information; the RS detecting aninitial ranging code from the MS; the RS sending a response to thereceived initial ranging code.

In some embodiments, the initial ranging code received by the RScomprises: an initial ranging code selected from a set of RS dedicatedinitial ranging codes that are specific to different RSs respectively ina cell served by the BS.

In some embodiments, information regarding RS dedicated initial rangingcodes is transmitted and readable by all receivers within range of theBS on a BS broadcast channel.

In some embodiments, initial ranging code received by the RS comprises:an initial ranging code selected from a set of allocated common initialranging codes that are used for the BS and all RSs in a cell served bythe BS.

According to an aspect of the invention, there is provided in an OFDMsystem comprising a base station (BS), at least one relay station (RS)and a plurality of mobile station (MSs), a method comprising: an RSreceiving a BS preamble and additional information from the BS in a BSdownlink (DL) transmission, the additional information including aBS-FCH (BS frame control header), BS-MAP (BS-multiplexing accessprofile), BS-Broadcast information; the RS transmitting in an RS DLtransmission an RS preamble and an RS-FCH (RS frame control header),RS-MAP (RS-multiplexing access profile) and the BS-Broadcast informationfollowing a duration for receiving the additional information receivedfrom the BS in the BS DL transmission; the at least one RS receiving inan RS UL transmission ranging information from any relay stations andMSs with which the at least one RS is communicating; the at least one RStransmitting in a BS UL transmission ranging information from the atleast one relay station (RS) and at least some of the plurality of MSs.

In some embodiments, the method further comprises separating ULtransmissions from DL transmissions using TDD (time division duplexing).

In some embodiments, the method further comprises defining TDD frames,each TDD frame comprising a DL sub-frame during which downlinktransmissions for the BS and RSs takes place, and a UL sub-frame duringwhich uplink transmissions to the BS and RSs takes place, the DLsub-frame and the UL sub-frame being sequentially transmitted.

In some embodiments, the method further comprises separating ULtransmissions from DL transmissions using FDD (frequency divisionduplexing).

In some embodiments, the method further comprises defining FDD frames,each FDD frame comprising a DL frame during which downlink transmissionsfor the BS and RSs takes place, and a UL frame during which uplinktransmissions to the BS and RSs takes place, the DL frame and the ULframe being simultaneously transmitted using a different frequencyresource.

In some embodiments, the duration is the duration for the RS to receivethe additional information from the BS plus a predetermined offset.

In some embodiments, the duration is a fixed duration.

In some embodiments, a duration for receiving the additional informationis variable in duration.

According to an aspect of the invention, there is provided in an OFDMsystem comprising a base station (BS), at least one relay station (RS)and a plurality one mobile station (MS), a method comprising:communicating between the BS and an RS using closed-loop MIMO (multipleinput multiple output) techniques; and the RS communicating with atleast one MS of the plurality of MS.

In some embodiments, the RS communicating with at least one MS comprisescommunicating between the RS and the at least one MS using closed-loopMIMO techniques.

In some embodiments, the method further comprises: the RS communicatingwith at least one other RS; and the at least one other RS communicatingwith at least one MS of the plurality of MS.

In some embodiments, the RS communicating with at least one other RScomprises communicating between the RS and the at least one RS usingclosed-loop MIMO techniques.

According to an aspect of the invention, there is provided in an OFDMsystem comprising a base station (BS), at least one relay station (RS)and a plurality of mobile stations (MSs), a method comprising: for twoor more of a group consisting of: the BS; the at least one RS; and atleast one of the plurality of MSs: using a same set of sub-carriers fordownlink (DL) and/or uplink (UL) transmissions.

In some embodiments, the method further comprises transmitting betweenthe BS and at least one MS one hop from the BS and between the BS and atleast one RS one hop from the BS over respective sub-channels havingdifferent sub-carrier to sub-channelization permutations.

In some embodiments, the method further comprises transmitting betweenthe RS and at least one MS one hop from the RS over respectivesub-channels having different sub-carrier to sub-channelizationpermutations.

In some embodiments, the method further comprises for uplinktransmissions, one or both of: at least two MS, each respectively onehop from the BS, collaboratively transmitting to the BS; and at leasttwo MS, each respectively one hop from a respective RS, collaborativelytransmitting to the respective RS.

In some embodiments, the method further comprises for uplinktransmissions, one or both of: at least two RS, each one hop from theBS, collaboratively transmitting to the BS; and at least two MS, eachone hop from a respective RS, collaboratively transmitting to the RS.

In some embodiments, the method further comprises one or more of:transmitting concurrently from two or more RSs to the BS; transmittingconcurrently from two or more MSs to the BS; transmitting concurrentlyfrom two or more mobile stations to the at least one RS.

In some embodiments, the method further comprises performinginterference cancellation techniques to improve detection performance.

In some embodiments, performing interference cancellation techniques isperformed by one or both of the RS and the BS.

According to an aspect of the invention, there is provided a method forinserting OFDM pilot symbols in a time-frequency resource in a systemusing relay stations (RSs), at least one RS having N transmittingantennas, where N>=1 comprising: inserting pilot symbols in time andfrequency for each of the N transmitting antennas in a given relaystation in symbol locations that are not assigned to pilot symbols usedby a base station (BS) serving a cell in which the given RS is currentlylocated or mobile stations (MSs) located in the cell served by the BS.

In some embodiments, when N=2: for each transmitting antenna, assigningpilot symbols in time and frequency in a given pattern for transmissionby the antenna and assigning null symbol locations that correspond tolocations of pilot symbols to be transmitted by the other antenna.

In some embodiments, when N=4: for each transmitting antenna, assigningpilot symbols in time and frequency in a given pattern for transmissionby the antenna and assigning null symbol locations that correspond tolocations of pilot symbols to be transmitted by the other antennas.

In some embodiments, the method further comprises inserting OFDM pilotsymbols in a time-frequency transmission resource for other RSs in thesame cell with a pattern that is the same as a pattern of thetransmission resource of the given RS, but which is shifted in timeand/or frequency with respect to the given RS.

In some embodiments, inserting pilot symbols in time and frequencycomprises inserting pilot symbols in time and frequency using partialuse sub-carrier channelization (PUSC) and/or optional PUSC.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theattached drawings in which:

FIG. 1 is a block diagram of an example of a network including a basestation, relay stations and mobile stations;

FIG. 2 is a flow chart for a relay station (RS) initial access procedurein accordance with an embodiment of the invention;

FIG. 3 is a flowchart for a mobile station (MS) initial access procedurein accordance with an embodiment of the invention;

FIG. 4 is a set of schematic diagrams of a TDD (time division duplex)Frame Structure for a base station (BS) and an RS where a BS-FCH (basestation frame control header) reaches all MSs within range of the BS inaccordance with an embodiment of the invention;

FIG. 5 is a set of schematic diagrams of a TDD Frame Structure for a BSand an RS where a BS-FCH may not reach one or more MS, in accordancewith an embodiment of the invention;

FIG. 6 is a schematic diagram of concurrent transmissions occurring in adown link (DL) direction including BS to RS and RS to MS;

FIG. 7 is a schematic diagram of concurrent transmissions occurring inan up link (UL) direction including MS to RS and RS to BS;

FIG. 8 is a schematic diagram of a collaborative transmission occurringfor two RS communicating with a single BS;

FIG. 9 is a schematic diagram of a network for the purpose of showingwhen an interference cancellation scheme may be used according to someembodiments of the invention;

FIGS. 10a and 10b are a set of schematic diagrams of RS pilot designsfor a particular type of sub-carrier to sub-channel allocation (partialuse sub-channelization (PUSC)) for UL transmission using a singletransmission antenna RS in accordance with an embodiment of theinvention;

FIG. 11 is a set of schematic diagrams of RS pilot design for PUSC forUL transmission using a two transmission antenna RS in accordance withan embodiment of the invention;

FIGS. 12a, 12b and 12c are schematic diagrams of RS pilot designs forPUSC for UL transmission using a four transmission antenna RS inaccordance with an embodiment of the invention;

FIGS. 13a and 13b are a set of schematic diagrams of RS pilot designsfor another type of sub-carrier to sub-channel allocation (optional PUSC(OPUSC)) for UL transmission using a single transmission antenna RS inaccordance with an embodiment of the invention;

FIGS. 14a and 14b are a set of schematic diagrams of RS pilot designsfor OPUSC for UL transmission using a two transmission antenna RN inaccordance with an embodiment of the invention;

FIG. 15 is a set of schematic diagrams of RS pilot designs for OPUSC ULtransmission UL transmission using a four transmission antenna RS inaccordance with an embodiment of the invention;

FIGS. 16 through 19 are diagrams of frame structures provided byembodiments of the invention;

FIGS. 20 and 21 are schematic diagrams of frame structures provided byembodiments of the invention;

FIG. 22 is a set of schematic diagrams of schematic diagrams of binconstruction for even and odd bin sizes;

FIG. 23 is a set of schematic diagrams of two specific sub-channeldefinitions;

FIG. 24 is a schematic diagram of a frame structure according to anembodiment of the invention;

FIG. 25 shows specific examples of bin definitions for two different binsizes, and for bins with and without pilots;

FIG. 26 is a set of schematic diagrams of two specific sub-channeldefinitions;

FIG. 27 is a group of schematic diagrams of pilot patterns to be used byan RS according to some embodiments of the invention;

FIG. 28 is a block diagram of a cellular communication system;

FIG. 29 is a block diagram of an example base station that might be usedto implement some embodiments of the present invention;

FIG. 30 is a block diagram of an example wireless terminal that might beused to implement some embodiments of the present invention;

FIG. 31 is a block diagram of a logical breakdown of an example OFDMtransmitter architecture that might be used to implement someembodiments of the present invention;

FIG. 32 is a block diagram of a logical breakdown of an example OFDMreceiver architecture that might be used to implement some embodimentsof the present invention; and

FIG. 33 is a block diagram of functionality in a base station forfacilitating intra-cell peer-to-peer communication.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

In accordance with embodiments of the invention, various physical layerdesigns and procedures are provided for enabling relay basedcommunications that may find applications in an IEEE 802.16 basednetwork. The concepts described herein are not, however, limited in thisregard and may be applicable to any OFDM based systems, such as 3GPP and3GPP2 evolutions.

FIG. 1 shows an example of a wireless system, for example an OFDMnetwork that includes relays. Shown is a base station (BS) 130 that isin communication with one or more mobile stations (MS), only one shownMS-1 132, and one or more first tier relay stations (RS), only one shownRS-1 138. Some of the first tier (one hop away from BS) relay stationsare in communication with one or more second tier (two hops away fromBS) relay stations. RS and MS the same number of hops away from the BSare said to be in the same tier. In the illustrated example RS-1 138 isin communication with second tier RS-2 140. Each relay station can serveone or more mobile stations. For example, RS-1 138 is in communicationwith MS-2 134 and RS-2 140 is in communication with MS-3 136. In theparticular example, there is a two-tier relay structure, such that thereis a maximum of three hops to reach a mobile station. Larger numbers ofhops are contemplated. Furthermore, the specific network of FIG. 1 is tobe considered only an example. More generally, an arbitrary arrangementof base stations, relay stations, and mobile stations is contemplated.The mobile stations will change over time due to their mobility. Someembodiments support only fixed relays; others support mobile relays,while further embodiments support both fixed and mobile relays.

When a relay station is added to a wireless system, the RS initiallyaccesses the system by communication with a base station. Referring toFIG. 2, a method for initial access for a relay station will now bedescribed. In the interest of brevity, this flowchart includes stepsexecuted by a BS and steps executed by an RS. Note that furtherembodiments of the invention provide a method consisting only of the RSexecuted stations, and an RS operable to execute such a method, and amethod consisting only of the BS executed steps, and a BS operable toexecute such a method. The RS performs down link (DL) synchronization,which includes frame synchronization and timing/frequencysynchronization at step 200. For example, the RS receivessynchronization information sent by the BS that any RS (or MS) withinreceiving distance of the BS is capable of receiving, for example a BSDL common Sync symbol and/or BS preamble information. At step 210, cellidentification and selection is performed by the RS. This results in aspecific BS being selected by the RS as the one to access the systemthrough. At step 220, system parameters are obtained and decoded by theRS from information sent on a broadcast channel by the BS and capable ofbeing read by all receiving stations, either RS or MS. At step 230, theRS performs initial ranging. This includes the RS sending an initialranging code. This code may be one of a set of predeterminedpseudo-noise codes allocated for requesting initial access to the BS. Atstep 240, the BS detects the RS initial ranging code. At step 250, theBS responds to the received initial ranging code sent by the RS. A linkis then established between the BS and the RS as indicated at 260.

In a network with no relay stations, a set of ranging codes is allocatedfor the MSs for initial ranging. In a network with relay stations,ranging codes also need to be allocated to RSs for initial ranging.There are multiple ways to allocate ranging codes to RSs and MSs.

In some embodiments, a set of ranging codes that are used for initialaccess ranging is separated into two sub-sets, and one subset isassigned to be used by RSs and the other sub-set is assigned to be usedby MSs for initial ranging of RSs and the BS. In some embodiments, thesame ranging codes are used for both RSs and MSs for initial accessranging. In such embodiments, the BS is able to distinguish betweenranging by the RSs and MSs. In some embodiments, differenttime-frequency transmission resources are used for RS initial rangingthan are used for MS initial ranging.

Referring to FIG. 3, a method for a mobile station to initially access anetwork having a BS and at least one RSs will now be described. In theinterest of brevity, this flowchart includes steps executed by a BS/RSand steps executed by a MS. Note that further embodiments of theinvention provide a method consisting only of the BS/RS executed steps,and a BS/RS operable to execute such a method, and a method consistingonly of the MS executed stations, and a MS operable to execute such amethod.

At step 300, the MS performs initial system access to synchronize withaccess points (AP) in the network, which includes frame synchronizationand timing/frequency synchronization. An access point is an RS or the BSof the cell serving the MS that the MS accesses when entering thenetwork. In some embodiments, this includes the BS transmitting a DL BScommon Sync symbol and preamble and the RS transmitting a DL RS commonSync symbol and preamble. The DL BS and DL RS common Sync symbols may becarried on respective BS and RS common Sync channels transmitted by theRS and BS, respectively.

In some embodiments, the DL RS common Sync symbol is identical instructure and sequence to that which is transmitted by the BS, asdescribed above, with regard to the RS initially accessing the network.

The preamble transmitted by each AP may include an AP specific Syncchannel. In some embodiments, the preamble transmitted by the RS issimilar to a BS cell specific Sync channel in a system not using relaystations. In some embodiments, the preamble transmitted by the RS mayuse an identical structure to that used by the BS. In some embodiments,an RS signature for the RS is added to the AP specific Sync channel. TheRS may obtain its signature from the BS. In some embodiments, the RSspecific code is added on top of a cell specific code. In someembodiments, RS specific scrambling is applied to cell specific codes.

At step 310, the MS performs AP identification and selection based onthe DL AP common Sync symbol and preamble. In some embodiments, this isa similar procedure to cell identification and selection that the MSperforms with the BS in non-relay systems or that the RS performs withthe BS as described above with regard to FIG. 2. In someimplementations, a two-step preamble detection is performed in which theMS performs cell identification and selection and then the MS performsAP identification and selection in the selected cell. In someimplementations, a one-step preamble detection is performed in which theMS scans all cell specific codes and selects the AP based on the resultsof scanning. For example, the MS might select the AP with the strongestreception. In some embodiments, a threshold value for the signalstrength of the measured preamble can be set to trigger the selection ofRS. Cell selection involves selecting a single AP from a set of one ormore RSs and/or BSs that are detected.

At step 320 the MS obtains and decodes system parameters frominformation sent on a broadcast channel by the selected access point (RSor BS). In the event the RS transmits a broadcast channel, the RS mayretransmit information passed along from the BS. Alternatively, for theRS case, rather than the RS transmitting a broadcast channel, the systeminformation may be obtained from a broadcast channel sent by the BS.

At step 330, the MS performs initial ranging. The MS sends an initialranging code to the selected access point (RS or BS). Alternatively orin addition, in the RS case, the ranging code may be sent directly tothe BS. If initial ranging codes are sent to both the BS and theselected RS, coordination of transmissions may be needed.

Following the MS sending the initial ranging code at step 330, the APsin the cell detect the initial ranging code at step 340.

At step 350, the selected AP (BS or RS), sends a response to thereceived initial ranging code sent by the MS. A link is then establishedbetween the selected AP (BS or RS) and the MS as indicated at 360.

There are multiple ways of performing steps 330 and 340. In a firstexample of the MS performing initial ranging, BS and RS dedicatedinitial ranging codes are used. For initial ranging to RSs for example,each RS is assigned an RS initial ranging code from a set of RS initialranging codes to distinguish between different RSs in the same cell. TheMS may obtain RS initial ranging code information from the BS broadcastchannel.

The initial ranging code is then detected by the selected AP (BS or RS).In the RS case, the RS detects its dedicated initial ranging code. TheRSs pass the detected information to the BS. The BS determines RSselection results based on the dedicated initial ranging code.

In a second example, common initial ranging codes are used for the BSand all RSs in the same cell. In some embodiments, the ranging codes inthe 802.16e standard may be used. The common initial ranging code sentby the MS is detected by the RSs. In some embodiments, all RSs in thesame cell may detect an initial ranging channel on which the commoninitial ranging code is transmitted. The RS passes the detectedinformation to the BS. The BS receives MS's RS selection informationfrom message exchanges between the MS and the RS as well as between theRS and the BS.

FIGS. 2 and 3 are described in relation to a single hop between the RSand BS and a single hop between the MS and the RS. However, a relaystation entering a network more than a single hop from the BS or a MSattaching to a multiple hop series of RSs are also contemplated.

A transmission resource for OFDM transmission is a two dimensionalresource. A first dimension consists of a set of OFDM sub-carriers. Asecond dimension consists of OFDM symbols, an OFDM symbol referring tothe transmission of OFDM sub-carriers collectively for an OFDM symbolduration. Sets of OFDM symbols may also be combined to form frames.Another way of defining the two dimensional OFDM resource is to considerone dimension to be represented by logical sub-channels and the otherdimension is represented by sub-channel allocation periods which may beone or multiple OFDM symbols.

FIG. 4 illustrates examples of respective TDD (time division duplex)frame structures for use by a BS and for use by an RS. The BS framestructures of FIG. 4 include an example DL sub-frame 400 and ULsub-frame 420 for transmission between the BS and RS, as well as betweenthe BS and any MSs the BS may communicate with directly. The RS framestructures of FIG. 4 include an example DL sub-frame 440 and ULsub-frame 460 for transmission between the RS and MSs and between the RSand other RSs with which the RS may communicate. For the examples ofFIG. 4, it is assumed that a frame control header (FCH) transmitted bythe BS is received by all MSs in the cell served by the BS. The FCHprovides some initial information about the contents of the DL and/or ULsub-frames. For example, the FCH may contain information about the sizeof the multiplexing access profile (MAP) information following the FCH.The MAP information is used to identify locations in the DL sub-framewhere data is transmitted to particular RSs or MSs and/or locations inthe UL sub-frame where data is received from particular RSs or MSs.

The sub-frames that are depicted in FIG. 4 are two dimensional channelresources in which one dimension is represented by logical sub-channelsand the other dimension is represented by sub-channel allocation periodswhich may be one or multiple OFDM symbols. A logical sub-channel is adesignated grouping of active sub-carriers that may or may not becontiguous, and that may not necessarily all be on the same OFDM symbol.Active sub-carriers are any one of data sub-carriers for datatransmission, pilot sub-carriers for synchronization, or sub-carriersthat do not involve direct transmission, but are used for example astransition guards between the sub-frames. In some embodiments, acombination of the DL and UL sub-frames 400,420 form a frame thatenables two-way communication between the BS and one or more RS and theBS and one or more MS. In use, such a frame is preceded and followed bysimilar frames, all forming part of an ongoing sequence of frames. Insome embodiments, a combination of the DL and UL sub-frames 440,460 forthe RS form a frame that enables two-way communication between the RSand one or more RS and the RS and one or more MS. In use, such a frameis preceded and followed by similar frames, all forming part of anongoing sequence of frames.

In some embodiments, for each of the BS and the RS, each DL sub-frame400,440 starts with a respective preamble 402,442. In the BS DLsub-frame 400, following the preamble 402, the BS includes a framecontrol header (FCH) [BS-FCH] 404 described above that is capable ofbeing received and read by all stations, either RS or MS, within thetransmission range of the BS. Following the BS-FCH 404, the BS DLsub-frame 400 includes a multiplexing access profile (MAP) [BS-MAP] 406that is also capable of being received and read by all stations, eitherRS or MS, within the transmission range of the BS. In some embodiments,the BS also transmits information in a broadcast format [BS-Broadcast]that can be detected by all who receive it. In some embodiments, aportion of the DL sub-frame 400 is allocated for transmission of theBS-Broadcast and the BS-MAP, as illustrated in FIG. 4. In someembodiments, each of the preamble 402, BS-FCH 404, BS-MAP andBS-Broadcast 406 vary in duration depending on their respective content.MSs that receive the DL structure 400 may know the length of BS-MAP 406even though it cannot decode information included in the BS-MAP 406. Thelength of the BS-MAP may be included in the BS-FCH, for example. An RSthat receives the DL sub-frame 400 decodes the BS-Broadcast informationand then retransmits it to other RS or MS. Also included in the BS DLsub-frame 400 is the BS-Traffic 408 to be transmitted to RSs and MSs. Insome embodiments, the portion of the BS DL sub-frame 400 including theBS-Traffic 408 may also include MAP information only accessible by areceiving station that knows its location or MAP information assignedonly for specific receiving stations.

In the RS DL sub-frame 440, following preamble 442 the RS includes anull period 444 to allow receipt of the BS-FCH, BS-MAP and BS-Broadcast.The null period 444 may include a predetermined time offset (Δt) from apoint in time following the end of receipt of the BS-MAP andBS-Broadcast 406 to allow for RS radio switching from a receiving modeto a transmitting mode for example. In some embodiments, the inclusionof the predetermined time offset may aid in accommodating coexistence ofmultiple radios. The RS then transmits an RS specific FCH (RS-FCH) 446,RS specific MAP (RS-MAP) and broadcast format information [BS-Broadcast]448. The RS-FCH 446 and RS-MAP and BS-Broadcast 448 are received by MSsand other RSs that are in communication with the RS. The RS then sendtraffic 449 to the MSs or other RSs.

An MS receiving from a given RS may determine the location of the RS-FCHbased on the length of BS-FCH and Δt and then decode the RS-FCH andRS-MAP received from the given RS. This requires every MS, even thosereceiving access through an RS, to be able to receive enough of the BStransmission to determine where the RS-FCH is located.

In some embodiments, for each of the BS and the RS, each UL sub-frame420,460 may start with a ranging portion 422,462. Following the rangingportion 422,462 traffic 424,464 from the MS to the RS can be sent. Theranging portion may be used for example for initial ranging, periodicranging (for example to re-synchronize with the RS) or to transmitbandwidth requests.

FIG. 5 includes further examples of TDD frame structures for use in abase station and relay station. FIG. 5 includes an example DL sub-frame500 and UL sub-frame 520 for transmission between the BS and RS, as wellas between the BS and any MS the BS may communicate with directly. FIG.5 also includes an example DL sub-frame 540 and UL sub-frame 560 fortransmission between the RS and MSs and between the RS and other RSswith which the RS may communicate. For the examples of FIG. 5, every MSdoes not necessarily need to be able to receive something (the BS-FCH inthe FIG. 4 example) from the BS.

The BS DL and UL sub-frames 500,520 and the RS UL sub-frame 560 of FIG.5 have a similar structure to BS DL and UL sub-frames 400,420 and the RSUL sub-frame 460 described above with regard to FIG. 4.

RS DL sub-frame 540 includes a preamble 542. RS DL sub-frame 540 alsoincludes a null period 544 having a predetermined fixed offset from theend of the preamble 542. The use of the fixed offset allows the MS toknow the location of the RS-FCH without receiving anything from the BS.The null period 544 allows a duration during the DL sub-frame 540 forreceipt of the BS-FCH, BS-MAP and BS-Broadcast from the BS DL sub-frame500. The RS then transmits an RS specific FCH (RS-FCH) 546, RS specificMAP (RS-MAP) and broadcast format information [BS-Broadcast] 548. The RSthen sends traffic 449 to the MSs or other RSs.

An MS receiving the DL sub-frame 540 from a given RS may determine thelocation of the RS-FCH 546 based on the predetermined fixed offset andthen decode the RS-FCH 546 and the RS-MAP and BS-Broadcast 548 from thegiven RS.

For FIGS. 4 and 5 above it is assumed that there is only a single radioin the RS, which is why the RS DL sub-frame has the null period 449,549.The RS can not receive and transmit at the same time, therefore whilethe RS is receiving the BS-FCH, BS-MAP and BS-Broadcast information fromthe BS it cannot transmit to other RS or MS. However, in otherimplementations, the RS may include more than a single radio and as aresult the RS could receive and transmit at the same time. In someimplementations, for a multiple radio RS, the frame structure describedabove could still be used, however other more efficient frame structuresare also contemplated.

The embodiments described above, and the specific examples thereof shownin FIGS. 4 and 5 assume a TDD separation between DL and ULtransmissions. Further embodiments are provided that parallel theembodiments described with the exception that the separation between DLand UL transmission uses FDD (frequency division duplexing). All of theexamples described above also can be modified to this context; the onlydifference is that rather than having UL sub-frames and DL sub-framesthat are transmitted during separate time intervals, UL frames and DLframes are simultaneously transmitted, but on different frequencies.

Given that additional channel resources may be needed to maintain a linkbetween BS and RS, overall performance improvement of the system may beimpacted. Thus, schemes for enhancing spectrum efficiency according tosome embodiments of the invention are described below.

A first approach that can be exploited to possibly mitigate the effectof additional overhead introduced by communication between BS and RS isclosed-loop MIMO (multiple input multiple output). MIMO communicationinvolves transmissions between pairs of stations that each have multipleantennas or collaborative transmissions from multiple single antennastations to a multiple antenna station. The latter is known ascollaborative MIMO. Closed-loop MIMO includes the use of feedbackbetween the stations. Examples of implementation techniques forclosed-loop MIMO can be found in PCT International Patent ApplicationNo. PCT/CA2005/000506, assigned to the assignee of the presentapplication and incorporated herein by reference in its entirety. Theuse of closed-loop MIMO on the link between the BS and the RS mayimprove channel performance between the BS and RS. Closed-loop MIMO mayenable a reduction in DL and/or UL transmit power for the link betweenthe BS and RS.

When using closed-loop MIMO, a fixed relay station has multiple transmitantennas and multiple receive antennas although the transmit antennasand receive antennas are not necessarily distinct. In someimplementations, a link between two fixed location stations, for examplea fixed location BS and a location fixed RS, aids in making closed-loopMIMO and signal processing techniques used over the link reliable.

A second approach that can be exploited to possibly mitigate theoverhead introduced by the communications between BS and RS is aspectrum sharing scheme that may enhance the spectrum efficiency of thesystem. The spectrum sharing scheme may include one or more of a)concurrent transmissions from two or more RSs to a BS, b) concurrenttransmissions from two or more MS to an RS and RS to BS, and c)interference cancellation to improve detection performance.

For concurrent transmissions, the transmission resources being used areat least partially the same for respective transmission sources. Forexample, two RS that are each one hop away from the BS and use the sameband of sub-carriers to communicate with the BS are performing spectrumsharing.

Interference cancellation may be done at either of the BS and the RS inorder to deal with the effects of multiple signals being transmittedusing the same spectrum. The spectrum sharing scheme may also utilizepower control techniques between the BS and RS, depending on the qualityof the link.

Referring now to FIG. 6, an example of how closed-loop MIMO can be usedbetween a multiple antenna BS and a multiple antenna RS and between amultiple antenna RS and a multiple antenna MS for DL transmission willnow be described. FIG. 6 illustrates a multiple hop network 600including a BS 605 having multiple antennas, three multiple antennarelay stations RS-1 610, RS-2 630, RS-3 640 and multiple mobile stationsMS-1 620, MS-2 625, MS-3 632, MS-4 636, MS-5 642, MS-6 646. DLtransmissions are occurring simultaneously over different hops of themultiple hop network 600. The BS 605 is shown to be in communicationwith RS-1 610 via a closed-loop MIMO link 615. The BS 605 is also shownin communication with MS-1 620 via link 618. BS 605 has a sufficientnumber of antennas to allow it to perform MIMO processing of signalsfrom RS-1 610 and MS-1 620, as well as any other RS or MS it may be incommunication with. MS-1 620 has only a single antenna so link 618 isnot a closed-loop MIMO link. The links between BS 605 and RS-1 610 andBS 605 and MS-1 620 are formed over different sub-channels. The linksbetween BS 605 and RS-1 610 and between BS 605 and MS-1 620 areindicated to be different DL sub-channels according to legend 602

RS-2 630 and RS-3 640 are each respectively shown in communication withMSs over different respective DL sub-channels simultaneous with thecommunication occurring between BS 605 and RS-1 610 and BS 605 and MS-1620. RS-2 630 is communicating with MS-3 632 and MS-4 636 over links 634and 638, respectively. RS-3 640 is communicating with MS-5 642 and MS-6646 over links 644 and 648, respectively. MS-6 has two antennas (notshown) enabling closed-loop MIMO to be used over link 648. RS-3 640 hasa sufficient number of antennas to allow it to perform MIMO processingof signals from MS-5 642 and MS-6 646. The links between RS-2 630 andMS-3 632 and MS-4 636 and between RS-3 640 and MS-5 642 and MS-6 646 areindicated to be different DL sub-channels according to legend 602.

In the illustrated example at another time, a closed-loop MIMO link mayexist (not shown) for DL communication between RSs that are one hopapart, for example RS-1 610 and RS-2 630.

Different permutations may be applied for links between BS and RS and RSand MS. A permutation is a particular mapping of sub-carriers into alogical sub-channel.

Referring now to FIG. 7, an example of how closed-loop MIMO can be usedbetween a multiple antenna RS and a multiple antenna BS and between amultiple antenna RS and a multiple antenna MS for UL transmission willnow be described. Furthermore, FIG. 7 also illustrates how collaborativeMIMO can be used between two or more single antenna MS and a multipleantenna RS and between two or more single antenna MS and a multipleantenna BS, for UL transmissions. FIG. 7 illustrates a multiple hopnetwork 700 including a BS 705 having multiple antennas, three multipleantenna relay stations RS-1 710, RS-2 730, RS-3 740 and multiple mobilestations MS-1 720, MS-2 725, MS-3 731, MS-4 732, MS-5 735, MS-6 736,MS-7 741, MS-8 742 MS-9 745, MS-10 746, MS-11 749. UL transmissions areoccurring simultaneously over different hops of the multiple hop network700. BS 705 is shown to be in communication with RS-1 710 via aclosed-loop MIMO link 715. BS 705 is also shown in communication withMS-1 720 and MS-2 725 using collaborative MIMO. The links between BS 705and RS-1 710 and BS 605 and both MS-1 720 and MS-2 725 are formed overdifferent sub-channels as indicated by legend 702.

In the illustrated example at another time, a closed-loop MIMO link mayexist (not shown) for UL communication between RSs that are one hopapart, for example RS-1 610 and RS-2 630.

RS-2 730 and RS-3 740 are each respectively shown in communication withpairs of MS using collaborative MIMO over different respective ULsub-channels. RS-2 730 is communicating with MS-3 731 and MS-4 732 overcollaborative MIMO link 733 and with MS-5 735 and MS-6 736 overcollaborative MIMO link 737. RS-3 740 is communicating with MS-7 741 andMS-8 742 over collaborative MIMO link 743 and with MS-9 745 and MS-10746 over collaborative MIMO link 747. RS-3 740 is communicating withMS-11 748 via a closed-loop MIMO link 749. RS-3 740 has a sufficientnumber of antennas to allow it to perform MIMO processing of signals toall MS with which it is communicating. The links between RS-2 730 andMS-3 731 and MS-4 732 and between RS-2 730 and MS-5 735 and MS-6 736,the links between RS-3 740 and MS-7 741 and MS-8 742 and between RS-3740 and MS-9 745 and MS-10 746 and the link between RS-3 740 and MS-11748 are indicated to be different DL sub-channels according to legend702.

Different permutations may be applied for links between BS and RS and RSand MS.

In some embodiments, for concurrent transmissions of two multipleantenna RSs to the multiple antenna BS, collaborative MIMO isimplemented if channel conditions permit. FIG. 8 illustratescollaborative transmission in a UL direction over collective links 820for two RS, RS-1 810 and RS-2 815 with BS 805. Furthermore, in someembodiments, the BS may perform interference cancellation to mitigateinterference from sources other than the two RSs. In some embodiments,the BS has a larger number of antennas than the RSs. In someembodiments, one or more RS being served by the BS have an equal numberof antennas to that of the BS.

Referring now to FIG. 9, an example of how an interference cancellationscheme is used will be described. FIG. 9 illustrates a first multipleantenna RS RS-1 910 in UL communication with multiple antenna BS 905. Asecond multiple antenna RS RS-2 915 is attempting to receive ULtransmissions, which are being sent using collaborative MIMO by MS-1 930and MS-2 935. The UL transmission from RS-1 910 may interfere with thecollaborative MIMO transmissions of MS-1 930 and MS-2 935 to RS-2 915.Therefore, RS-2 915 may perform interference cancellation to mitigate,reduce and/or cancel interference from other RS, namely RS-1 in thisexample.

In some embodiments, channel information such as pilot symbols frominterfering stations is used to enable interference cancellation for agiven station. Examples of pilot symbol arrangements that can be used tosupport interference cancellation are described below in FIGS. 10-15.The pilot symbol arrangements can be used for UL transmissions from anRS to BS and UL transmissions from an RS to another RS.

To maintain backward compatibility with existing standards in the areaof wireless networks, for example 802.16e, the BS and MS may use theconventional pilot designs for their transmissions. The pilot symbols inthe pilot arrangements used by RSs may be orthogonal to the BS and MSpilots.

In some embodiments, different RSs in the same cell use different pilotpatterns, if multiple pilot patterns exist. The pilot patterns may beorthogonal to each other. In some embodiments, a design of an RS pilotarrangement supports collaborative MIMO for multiple RS. In someembodiments, for fixed RS, sub-band based sub-channelization is used ingenerating patterns that include pilot symbols.

In some embodiments of the invention, pilot overhead for fixed RS may bereduced as compared to pilot pattern designs used in the 802.16estandard.

In a particular implementation, a sub-carrier to sub-channel permutationmay include six contiguous groups of time-frequency resources to form asub-channel. A group of time-frequency resources is commonly known as atile and includes a band of sub-carriers being used for signaltransmission over a given number of OFDM symbols. The sub-carriers inthe band may be a group of contiguous frequencies or a logical groupingof non-contiguous frequencies. For example, a tile used in describingpilot patterns in FIGS. 10 through 12 is a band of four sub-carriersover three OFDM symbol durations.

FIGS. 10A and 10B show RS pilot patterns that might, for example, beused with systems employing a sub-carrier to sub-channelizationallocation known as UL PUSC (partial use sub-carrier channelization)with a single transmission antenna RS. In a PUSC allocation, fullchannel diversity is achieved by distributing allocated sub-carriers tosub-channels, whereby the allocated sub-carriers are a subset of theentire available bandwidth. FIG. 10A shows a particular tile structure1010 of an OFDM transmission resource having a two dimensionalappearance. Each horizontal row of the tile structure 1010 represents anOFDM symbol duration and each vertical column represents a differentsub-carrier. In the particular tile structure, pilot symbols are shownoccupying the four corners of the three OFDM symbol duration by foursub-carrier tile structure. This particular representation is a pilotpattern that may be used in systems complying with existing standardsand which are sometimes referred to as “legacy systems”, in which BS andMS communicate directly without an RS. The remaining eight symbollocations in the tile structure, collectively indicated at 1014 areidentified as being used for data.

Pilot patterns 1 through 8 are groups of six tiles each having threeOFDM symbol duration by four sub-carrier size that are concatenatedtogether in the frequency direction. Looking at a same given tile ineach of the eight patterns, a different single symbol location isidentified as being used for an RS pilot symbol in each respectivepattern. The locations used for the RS pilot symbol are the eight symbollocations not associated with legacy system pilots. In some embodiments,some or all of the eight different pilot pattern can be used fordifferent RSs in the same cell. If two RS in the same cell are separatedby a sufficient distance that interference is at or below an acceptablelevel, the same pattern can be used by both RS.

FIG. 11 shows a set of four example RS pilot patterns for UL PUSC usinga two transmission antenna RS. The tile structure is the same as thetile in FIG. 10A. The pilot patterns in FIG. 11 are also six tilesconcatenated together in the frequency direction as in FIGS. 10A and10B. In each respective pattern, locations are indicated where pilotsfor each of a first and a second antenna transmits its own pilot and anull symbol location in the location where the other antenna transmitsits pilot. The four patterns shown are not considered to be anexhaustive or complete list of possible pilot symbol arrangements.

FIGS. 12A, 12B and 12C show a set of five example RS pilot patterns forUL PUSC using a four transmission antenna RS. The tile structure is thesame as the tile in FIG. 10A. The pilot patterns in FIGS. 12A, 12B and12C are also six tiles concatenated together in the frequency directionas in FIGS. 10A and 10B. Each antenna transmits its own pilot and a nullsymbol locations in the locations where the other antennas transmittheir respective pilots. The five patterns shown are not considered tobe an exhaustive or complete list of possible pilot symbol arrangements.

The pilot patterns in FIGS. 10, 11 and 12 are described above as being agroup of six concatenated tiles of a particular size. More generally,the number of sub-carriers and OFDM symbol durations in a pilot patternis implementation specific. Furthermore, the locations of the legacypilots and RS pilots are examples of where such pilots may be locatedand other arrangements are contemplated. For example, a generalimplementation provides a tile design in which there is at least onepilot location for each antenna of a relay station that does notinterfere with pilot locations of the other antennas of the same relaystation, pilot locations of the BS, and pilot locations of other relaystations.

FIGS. 13A and 13B show RS pilot designs that might, for example, beapplied in systems employing another example sub-carrier tosub-channelization allocation scheme known as UL optional PUSC (OPUSC)in a single transmission antenna RS. In the example of UL OPUSCillustrated in FIG. 13A, a tile structure 1310 is three OFDM symboldurations by three sub-carriers in which a legacy pilot symbol 1312 isshown occupying the center location of the tile structure. Pilotpatterns 1-8 are groups of six three OFDM symbol duration by threesub-carrier tiles that are concatenated together in the frequencydirection. Looking at a same given tile in each of the eight patterns, adifferent single symbol location is identified as being used for an RSpilot symbol in each respective pattern. The locations used for the RSpilot symbol are the eight symbol locations not associated with thelegacy systems. A different pilot pattern can be used for different RSin the same cell. If two RS in the same cell are separated by asufficient distance that interference is at or below an acceptablelevel, a same pattern can be used by both RS.

FIGS. 14A and 14B show a set of example RS pilot patterns for ULoptional PUSC using a two transmission antenna RS. In the example of ULOPUSC illustrated in FIG. 14A, a tile structure 1410 is six OFDM symboldurations by three sub-carriers in which legacy pilot symbols 1412 arecollectively indicated at 1414. Pilot patterns 1-5 are groups of sixtiles that are concatenated together in the frequency direction. Lookingat a same given tile in each of the five patterns, two pairs of symbollocations are identified as being used for RS pilot symbols in eachrespective pattern. Each of a first and second antenna transmits its ownpair of pilots and a pair of null symbol locations in the locationswhere the other antenna transmits its respective pair of pilots. Thefive patterns shown are not considered to be an exhaustive or completelist of possible pilot symbol arrangements.

FIG. 15 shows a pair of example RS pilot patterns for UL optional PUSCusing a four transmission antenna RS. The tile structure is the same asthat of FIG. 14A. Pilot patterns 1 and 2 are groups of six tiles thatare concatenated together in the frequency direction. Looking at a samegiven tile in each of the two patterns, symbol locations are identifiedas being used for RS pilot symbols in each respective pattern. Each offirst, second, third and fourth antennas transmits its own pilot andnull symbol locations in the locations where the other antennas transmittheir respective pilots. The pair of patterns shown are not consideredto be an exhaustive or complete list of possible pilot symbolarrangements.

The pilot patterns in FIGS. 13, 14 and 15 are described above as being agroup of six concatenated tiles of a particular size. More generally,the number of sub-carriers and OFDM symbol durations in a pilot patternis implementation specific. Furthermore, the locations of the legacypilots and RS pilots are examples of where such pilots may be locatedand other arrangements are contemplated.

For UL PUSC, in some embodiments, the pilot pattern arrangements are ¼of the conventional pilot overhead for a single antenna RS; ½ of theconventional pilot overhead for two antenna RS; and the same asconventional pilot overhead for four antenna RS.

For UL optional PUSC, in some embodiments, the pilot patternarrangements are ½ of the conventional pilot overhead for a singleantenna RS; ½ or the same as conventional pilot overhead for two antennaRS; and the same as conventional pilot overhead for four antenna RS.

FIGS. 16-19 are examples of two sequential TDD frames in a potentialseries of frames in which a respective DL sub-frame and a respective ULsub-frame have been combined together to form each of the two TDDframes. The size of these sub-frames can be statically or dynamicallydefined.

MS/RS Zones

Downlink zones in the DL sub-frames are classified into three types:

1) DL_Common zone: a set of one or more OFDM symbols specificallytargeted for reception by both MS and RS (for example while the RS is atnetwork entry);

2) DL_RS zone: a set of one or more OFDM symbols specifically targetedfor reception by one or multiple RS;

3) DL_MS zone: a set of one or more OFDM symbols specifically targetedfor reception by one or multiple MS.

The DL common zone may include a preamble and FCH, similar to thatdescribed above in FIGS. 4 and 5. FIGS. 16-19 also include an 802.16eMAP in the DL common zone. The 802.16e MAP is implementation specificbased on 802.16e and may not be included as such in all embodiments.More generally, the DL MAP is used to identify locations in the DLsub-frame where data is transmitted to particular RSs or MSs.

Uplink zones are classified into three types:

1) UL_Common zone: a set of one or more OFDM symbols for receiving fromboth MSs and RSs (for example while the RS is at network entry);

2) UL_RS zone: a set of one or more OFDM symbols for receiving from oneor multiple RS;

3) UL_MS zone: a set of one or more OFDM symbols for receiving from oneor multiple MS.

Some embodiments provide for the reuse of OFDM symbols in multiplezones. Some embodiments provide for reuse between different tiers, whileothers provide for reuse within a tier. An example of reuse betweendifferent tiers in a hierarchical network is a BS transmitting duringOFDM symbol intervals, and an RS transmitting on the same OFDM symbolintervals assuming the transmissions will not interfere. Another exampleof reuse between different tiers in a hierarchical network is an RStransmitting during OFDM symbol intervals, and an RS in a different tiertransmitting on the same OFDM symbol intervals assuming thetransmissions will not interfere.

An example of reuse within a tier in a hierarchical network is an RStransmitting during OFDM symbol intervals, and another same tier RStransmitting on the same OFDM symbol intervals assuming thetransmissions will not interfere.

Frame Structure with MS/RS Zones First Embodiment

In a first embodiment, the allocation of resources is performed in a TDDmanner between the UL and DL. Within a TDD frame, there is a DLsub-frame that is only used for downlink transmission (be it from BS toRS, or RS to RS or RS to MS), and a UL sub-frame that is only used foruplink transmission (be it from MS to RS, RS to RS or RS to BS).

It is assumed that full use sub-carrier utilization is employed meaningthat a full set of available sub-carrier frequencies is used. Moregenerally, other sub-carrier to sub-channel permutations are possible.

A single OFDM band is used for both RS links (between BS and RS as wellas RS and RS) and MS links (between BS and MS as well as RS and MS). Inthis embodiment, the single OFDM band is on a single OFDM carrier.

In a specific example, within a DL sub-frame, each BS is allocated aDL_RS zone for transmitting to RSs and a DL_MS zone for transmitting toMSs. Each RS is allocated a DL_RS zone for transmitting to RSs if itneeds to transmit to a next RS (there may not always be one) and a DL_MSzone for transmitting to MSs.

Similarly, in a specific example, within a UL sub-frame, each BS isallocated a UL_RS zone for receiving from RSs and a UL_MS zone forreceiving from MSs. Each RS is allocated a UL_RS zone for receiving fromRSs if it needs to receive from a next RS (there may not always be one)and a UL_MS zone for receiving from MSs.

For this embodiment, there is no reuse among different tier RS, that isRSs that are a different number of hops from the BS and the BS. Thismeans that once OFDM symbols have been allocated as a DL_MS zone of aBS, that time is not available for use by the RSs; rather the RSs areidle during that time. In some implementations of this frame structure,reuse is allowed among the same tier RSs, that is RS that are a samenumber of hops from the BS.

A specific example of frame structures defined in this manner is shownin FIG. 16. FIG. 16 also includes an example of a network 1600 includingrelay stations RS-1 1618 and RS-2 1620, base station BS 1610 and mobilestations MS-1 1612, MS-2 1614 and MS-3 1616, similar to FIG. 1 toclearly illustrate the correspondence of the frame structure to the basestation BS and relay stations RS-1 and RS-2. The frame structure fromthe perspective of BS 1610 is generally indicated at 1630. The framestructure from the perspective of RS-1 1618 is generally indicated at1632. The frame structure from the perspective of the RS-2 1620 isgenerally indicated at 1634. In the example of FIG. 16, each arrowbetween BS and MS/RS and between RS and RS/MS, for example arrow 1650between BS 1610 and RS-1 1618, represents a transmission/reception usinga full OFDM band. Only the DL_RS zones, DL_MS zones, UL_MS zones andUL_RS zones as defined above are specifically shown in the illustratedexample in the interest of simplifying the figure. However, it is to beunderstood that each arrow 1650 has an associated resource allocated fortransmission (by a BS, RS or MS) with the same resource allocated forreception (by a BS, RS or MS). In the frame structure 1630 for the BS1610, for both DL and UL, portions of the frame structure that are notfilled represent idle time for the BS 1610. In the frame structure 1632for RS-1 1618, DL portions of the frame structure that are not filled,and are not opposite portions of the frame structure 1630 for the BS1610 allocated for transmission to RS-1 1618, represent idle time forRS-1 1618. Furthermore, UL portions of the frame structure 1632 that arenot filled represent idle time for RS-1 1618. In the frame structure1634 for RS-2 1620, DL portions of the frame structure that are notfilled, and are not opposite portions of the frame structure 1632 forRS-1 1618 allocated for transmission to RS-2 1620, represent idle timefor RS-2 1620. Furthermore, UL portions of the frame structure 1634 thatare not filled in and are not opposite portions of the frame structure1632 allocated for reception from RS-2 1620 represent idle time for theRS-2 1620.

In the illustrated example, two TDD frames 1660,1662 are shown. Only TDDframe 1660 will be described in detail. TDD frame 1660 is composed of aDL sub-frame 1664 during which all downlink transmissions occur and a ULsub-frame 1666 during which all uplink transmissions occur. A legendindicating differing shadings for the differing zone types is generallyindicated at 1668.

During the DL sub-frame 1664, the frame structure 1630 for the BS 1610includes a common zone 1670 for transmissions that can be received byMSs and RSs. The frame structure 1630 includes a DL_MS zone 1672 fortransmission directly to mobile stations such as MS-1 1612. There is aDL-RS zone 1676 that includes an R-MAP 1674 for transmission to relaystations such as RS-1 1618.

During the DL sub-frame 1664, the frame structure 1632 for the RS-1 1618includes a common zone 1682 for transmissions that can be received byMSs and RSs. The frame structure 1632 includes a DL_MS zone 1692 fortransmission directly to mobile stations such as MS-2 1614. There is aDL-RS zone 1690 that includes an R-MAP 1688 for transmission to relaystations such as RS-2 1620. There is also an RS radio switching period1684. During this time, the RS switches its radio from transmitting toreceiving. There is a second RS switching period 1686 during which theRS switches its radio from receiving to transmitting.

During the DL sub-frame 1664, the frame structure 1634 for the RS-2 1620includes a common zone 1613 for transmissions that can be received byMSs and RSs. The frame structure 1634 includes a DL_MS zone 1619 fortransmission directly to mobile stations such as MS-3 1616. There isalso an RS radio switching period 1615. During this time, the RSswitches its radio from transmitting to receiving. There is a second RSswitching period 1617 during which the RS switches its radio fromreceiving to transmitting.

During the UL sub-frame 1666, the frame structure 1630 for the BS 1610includes a UL RS zone 1678 for receiving from relay stations such asRS-1 1618, and a UL MS zone 1680 for receiving from mobile stations suchas MS-1 1612.

During the UL sub-frame 1666, the frame structure 1632 for the RS-1 1618includes a UL RS zone 1694 for receiving from relay stations such asRS-2 1620, and a UL MS zone 1696 for receiving from mobile stations suchas MS-2 1614. There is also an RS radio switching period 1693. Duringthis time, the RS switches its radio from transmitting to receiving.There is a second RS switching period 1698 during which the RS switchesits radio from receiving to transmitting.

During the UL sub-frame 1666, the frame structure 1634 for the RS-2 1620includes a UL MS zone 1621 for receiving from mobile stations such asMS-3 1616.

Frame Structure with MS/RS Zones Second Embodiment

In a second embodiment, the allocation of resources is again performedin a TDD manner between the UL and DL. Within a TDD frame, there is a DLsub-frame that is only used for downlink transmission (be it from BS toRS, or RS to RS or RS to MS), and a UL sub-frame that is only used foruplink transmission (be it from MS to RS, RS to RS or RS to BS).

It is assumed that full use sub-carrier utilization is employed meaningthat a full set of available sub-carrier frequencies is used. Moregenerally, other sub-carrier to sub-channel permutations are possible.

A single OFDM band is used for both RS links (between BS and RS as wellas RS and RS) and MS links (between BS and MS as well as RS and MS). Inthis embodiment, the single OFDM band is on a single OFDM carrier.

In a specific example, within a DL sub-frame, each BS is allocated aDL_RS zone for transmitting to RSs and a DL_MS zone for transmitting toMSs. Each RS is allocated a DL_RS zone for transmitting to RSs if itneeds to transmit to a next RS (there may not always be one) and a DL_MSzone for transmitting to MSs.

Similarly, in a specific example, within a UL sub-frame, each BS isallocated a UL_RS zone for receiving from RSs and a UL_MS zone forreceiving from MSs. Each RS is allocated a UL_RS zone for receiving fromRSs if it needs to receive from a next RS (there may not always be one)and a UL_MS zone for receiving from MSs.

For this embodiment, there is reuse among different tier BS and/or RS.This means, for example, that once OFDM symbols have been allocated as aDL_MS zone of a BS, that time is also made available for use by the RSs,assuming interference problems will not occur. In some implementationsof this frame structure, reuse is also allowed among the same tier RSs.

A specific example of frame structures defined in this manner is shownin FIG. 17, where a similar convention to showing the frame structure tothat used in FIG. 16 described above has been employed. FIG. 17 alsoincludes the example network 1600 of FIG. 16 to clearly illustrate thecorrespondence of the frame structure to the base station BS and relaystations RS-1 and RS-2. The frame structure from the perspective of BS1610 is generally indicated at 1736. The frame structure from theperspective of RS-1 1618 is generally indicated at 1738. The framestructure from the perspective of RS-2 1620 is generally indicated at1640. In the example of FIG. 17, each arrow for example arrow 1756between BS 1610 and RS-1 1618 represents a transmission/reception usinga full OFDM band.

In the illustrated example, two TDD frames 1760,1762 are shown. Only TDDframe 1760 will be described in detail. TDD frame 1760 is composed of aDL sub-frame 1764 during which all downlink transmissions occur and a ULsub-frame 1766 during which all uplink transmissions occur. A legendindicating differing shadings for the differing zone types is generallyindicated at 1768.

During the DL sub-frame 1764, the frame structure 1736 for the BS 1610includes a common zone 1770 for transmissions that can be received byMSs and RSs. The frame structure 1736 includes a DL_MS zone 1750 fortransmission directly to mobile stations such as MS-1 1612. There is aDL-RS zone 1754 that includes an R-MAP 1752 for transmission to relaystations such as RS-1 1618. There are also second and third DL_MS zones1746,1747 for transmission directly to mobile stations.

During the DL sub-frame 1764, the frame structure 1738 for the RS-1 1618includes a common zone 1782 for transmissions that can be received byMSs and RSs. The frame structure 1738 includes a DL_MS zone 1745 fortransmission directly to mobile stations such as MS-2 1614. There is aDL-RS zone 1744 that includes an R-MAP 1742 for transmission to relaystations such as RS-2 1620. There is also an RS radio switching period1784. During this time, the RS switches its radio from transmitting toreceiving. There is a second RS switching period 1786 during which theRS switches its radio from receiving to transmitting.

During the DL sub-frame 1764, the frame structure 1740 for the RS-2 1720includes a common zone 1713 for transmissions that can be received byMSs and RSs. The frame structure 1740 includes a DL_MS zone 1748 fortransmission directly to mobile stations such as MS-3 1616. There isalso an RS radio switching period 1715. During this time, the RSswitches its radio from transmitting to receiving. There is a second RSswitching period 1717 during which the RS switches its radio fromreceiving to transmitting. There is also a second DL_MS zones 1719 fortransmission directly to mobile stations.

During the UL sub-frame 1766, the frame structure 1736 for the BS 1610includes a UL RS zone 1778 for receiving from relay stations such asRS-1 1618, and a UL MS zone 1780 for receiving from mobile stations suchas MS-1 1612.

During the UL sub-frame 1766, the frame structure 1738 for the RS-1 1618includes a UL RS zone 1794 for receiving from relay stations such asRS-2 1620, and a UL MS zone 1796 for receiving from mobile stations suchas MS-2 1614. There is also an RS radio switching period 1793. Duringthis time, the RS switches its radio from transmitting to receiving.There is a second RS switching period 1798 during which the RS switchesits radio from receiving to transmitting.

During the UL sub-frame 1766, the frame structure 1740 for the RS-2 1620includes a UL MS zone 1721 for receiving from mobile stations such asMS-3 1616.

An example of reuse is illustrated for RS-1 1618 and BS 1610.Specifically, in frame structure 1738, R-MAP 1742 and DL RS zone 1744are transmitted at the same time as DL MS zone 1746 by BS 1610 in framestructure 1736. Another example is illustrated in which DL MS zone 1748is transmitted by RS-2 1620 in frame structure 1740 at the same time asDL MS zone 1750, RS-MAP 1752 and DL RS zone 1754 are transmitted by BS1610 in frame structure 1736. These are examples of reuse implementedbetween tiers.

Frame Structure with MS/RS Zones Third Embodiment

In a third embodiment, the allocation of resources is again performed ina TDD manner between the UL and DL. Within a TDD frame, there is a DLsub-frame that is only used for downlink transmission (be it from BS toRS, or RS to RS or RS to MS), and a UL sub-frame that is only used foruplink transmission (be it from MS to RS, RS to RS or RS to BS).

It is assumed that partial use sub-carrier channelization (PUSC) isemployed meaning that for some transmissions, a subset of an availableOFDM band is employed. For example, in some embodiments the availableOFDM band is divided into three parts, and the three parts can beallocated separately. More generally, separation into N parts may beperformed. The available OFDM band is divided during the DL sub-frameamong the BS and the RSs for transmission to respective MSs and the OFDMband is divided during the UL sub-frame among the BS and the RSs forreception from respective MSs.

A single carrier OFDM system involves an OFDM signal being modulatedonto a single carrier frequency. This OFDM band of the OFDM signal maybe still split into partial bands. In other embodiments described below,multiple different carrier frequencies are used, and a respective OFDMsignal is modulated onto each of the carriers.

For this embodiment, single carrier OFDM is used for both RS links(between BS and RS as well as RS and RS) and MS links (between BS and MSas well as RS and MS), although as indicated above, for PUSCimplementations, for some of these transmissions, only a part of theband is used.

In a specific example, within a DL sub-frame, each BS is allocated aDL_RS zone for transmitting to RSs and a DL_MS zone for transmitting toMSs. Each RS is allocated a DL_RS zone for transmitting to RSs if itneeds to transmit to a next RS (there may not always be one) and a DL_MSzone for transmitting to MSs.

Similarly, in a specific example, within a UL sub-frame, each BS isallocated a UL_RS zone for receiving from RSs and a UL_MS zone forreceiving from MSs. Each RS is allocated a UL_RS zone for receiving fromRSs if it needs to receive from a next RS (there may not always be one)and a UL_MS zone for receiving from MSs.

For this embodiment, there is no reuse among different tier BS and/orRS. In some implementations of this frame structure, reuse is allowedamong the same tier RSs.

A specific example of frame structures defined in this manner is shownin FIG. 18, where a similar convention to showing the frame structure tothat used in FIG. 16 described above has been employed. FIG. 18 alsoincludes the example network 1600 of FIG. 16 to clearly illustrate thecorrespondence of the frame structure to the base station BS and relaystations RS-1 and RS-2. The frame structure from the perspective of BS1610 is generally indicated at 1842. The frame structure from theperspective of RS-1 1618 is generally indicated at 1844. The framestructure from the perspective of RS-2 1620 is generally indicated at1846.

In the illustrated example, two TDD frames 1860,1862 are shown. Only TDDframe 1860 will be described in detail. TDD frame 1860 is composed of aDL sub-frame 1864 during which all downlink transmissions occur and a ULsub-frame 1866 during which all uplink transmissions occur. A legendindicating differing shadings for the differing zone types is generallyindicated at 1868.

During the DL sub-frame 1864, the frame structure 1842 for the BS 1610includes a common zone 1870 for transmissions that can be received byMSs and RSs. The frame structure 1842 includes a DL_MS zone 1854 fortransmission directly to mobile stations such as MS-1 1612. There is aDL-RS zone 1856 that includes an R-MAP 1858 for transmission to relaystations such as RS-1 1618.

During the DL sub-frame 1864, the frame structure 1844 for the RS-1 1618includes a common zone 1882 for transmissions that can be received byMSs and RSs. The frame structure 1844 includes a DL_MS zone 1830 fortransmission directly to mobile stations such as MS-2 1614. There is aDL-RS zone 1832 that includes an R-MAP 1836 for transmission to relaystations such as RS-2 1620. There is also an RS radio switching period1884. During this time, the RS switches its radio from transmitting toreceiving. There is a second RS switching period 1886 during which theRS switches its radio from receiving to transmitting. There is a thirdRS switching period 1887 during which the RS switches its radio fromtransmitting to receiving.

During the DL sub-frame 1864, the frame structure 1846 for the RS-2 1620includes a common zone 1813 for transmissions that can be received byMSs and RSs. The frame structure 1846 includes a DL_MS zone 1848 fortransmission directly to mobile stations such as MS-3 1616. There isalso an RS radio switching period 1815. During this time, the RSswitches its radio from transmitting to receiving.

During the UL sub-frame 1866, the frame structure 1842 for the BS 1610includes a UL RS zone 1878 for receiving from relay stations such asRS-1 1618, and a UL MS zone 1880 for receiving from mobile stations suchas MS-1 1612.

During the UL sub-frame 1866, the frame structure 1844 for the RS-1 1618includes a UL RS zone 1894 for receiving from relay stations such asRS-2 1620, and a UL MS zone 1896 for receiving from mobile stations suchas MS-2 1614. There is also an RS radio switching period 1893. Duringthis time, the RS switches its radio from receiving to transmitting.

During the UL sub-frame 1866, the frame structure 1846 for the RS-2 1620includes a UL MS zone 1821 for receiving from mobile stations such asMS-3 1616.

In the example of FIG. 18, each solid arrow 1850 as indicated in thelegend 1868 represents a transmission/reception using a portion of theOFDM band—⅓ in the particular example illustrated, while each dashedarrow 1852 as indicated in the legend 1868 represents thetransmission/reception using the full OFDM band. In the exampleillustrated, the partial band signals are used to transmit to and frommobile stations; thus, for the BS 1610, RS-1 1618 and RS-2 1620, eachare simultaneously allocated a third of the OFDM band at the same timeduring the DL sub-frame 1864 for transmission to MSs. Similarly, for theBS 1610, RS-1 1618 and RS-2 1620, each are simultaneously allocated athird of the OFDM band during the UL sub-frame 1866 for reception fromMSs. However, since the transmissions from BS to RS and RS to RS aretransmission/reception using the full OFDM band, and there is nofrequency reuse between tiers. Therefore, when a station is receiving atransmission it is not transmitting and vice versa.

Frame Structure with MS/RS Zones Fourth Embodiment

In a fourth embodiment, the allocation of resources is again performedin a TDD manner between the UL and DL. Within a TDD frame, there is a DLsub-frame that is only used for downlink transmission (be it from BS toRS, or RS to RS or RS to MS), and a UL sub-frame that is only used foruplink transmission (be it from MS to RS, RS to RS or RS to BS).

It is assumed that partial use sub-carrier utilization is employedmeaning that for some transmissions, a subset of an available OFDM bandis employed. For example, in some embodiments an available OFDM band isdivided into three parts, and the three parts can be allocatedseparately. More generally, separation into N parts may be performed.

For this embodiment, it is assumed there are multiple carriers employedmodulated by a respective OFDM signal having an OFDM band. For examplethere might be three carrier frequencies with respective OFDM bands thatcan be separately allocated. Note that a different OFDM band is distinctfrom portions of a single OFDM band; multiple portions of a single OFDMband transmitted by a single transmitter can be generated with a singleIFFT, but when multiple bands are employed, each needs a respectiveIFFT. These can be referred to as respective carriers (each carriercarrying a respective OFDM signal with the associated set ofsub-carriers). In a particular example, one OFDM carrier is used in apartial use manner for transmission to and from mobile stations with thebandwidth divided between the BS and RSs. In a particularimplementation, the BS is given ⅓ of a first carrier's band, first tierRSs are given ⅓ of the band, and second tier RSs are given ⅓ of the bandfor both uplink and downlink transmission; a second carrier's band isallocated for transmission by the BS to/from first tier RSs, and a thirdcarrier's band is allocated for transmission by first tier RSs to/fromsecond tier RSs. Transmissions on different carriers can take placesimultaneously as there is no interference; similarly transmissions ondifferent partial bands can take place as there is no interference.

A specific example of frame structures defined in this manner is shownin FIG. 19, where a similar convention to showing the frame structure tothat used in FIG. 16 described above has been employed. FIG. 19 alsoincludes the example network 1600 of FIG. 16 to clearly illustrate thecorrespondence of the frame structure to the base station BS and relaystations RS-1 and RS-2. The frame structure from the perspective of BS1610 is generally indicated at 1948. The frame structure from theperspective of RS-1 1618 is generally indicated at 1950. The framestructure from the perspective of RS-2 1620 is generally indicated at1952.

In the illustrated example, two TDD frames 1954,1956 are shown. Only TDDframe 1954 will be described in detail. TDD frame 1954 is composed of aDL sub-frame 1965 during which all downlink transmissions occur and a ULsub-frame 1966 during which all uplink transmissions occur. A legendindicating differing shadings for the differing zone types is generallyindicated at 1968.

During the DL sub-frame 1965, the frame structure 1948 for the BS 1610includes a common zone 1970 for transmissions that can be received byMSs and RSs. The frame structure 1948 includes a DL_MS zone 1930 fortransmission directly to mobile stations such as MS-1 1612. There is aDL-RS zone 1932 that includes an R-MAP 1934 for transmission to relaystations such as RS-1 1618.

During the DL sub-frame 1965, the frame structure 1950 for the RS-1 1618includes a common zone 1982 for transmissions that can be received byMSs and RSs. The frame structure 1950 includes a DL_MS zone 1940 fortransmission directly to mobile stations such as MS-2 1614. There is aDL-RS zone 1942 that includes an R-MAP 1944 for transmission to relaystations such as RS-2 1620.

During the DL sub-frame 1965, the frame structure 1952 for the RS-2 1620includes a common zone 1913 for transmissions that can be received byMSs and RSs. The frame structure 1952 includes a DL_MS zone 1946 fortransmission directly to mobile stations such as MS-3 1616.

During the UL sub-frame 1966, the frame structure 1948 for the BS 1610includes a UL RS zone 1978 for receiving from relay stations such asRS-1 1618, and a UL MS zone 1980 for receiving from mobile stations suchas MS-1 1612.

During the UL sub-frame 1966, the frame structure 1950 for the RS-1 1618includes a UL RS zone 1994 for receiving from relay stations such asRS-2 1620, and a UL MS zone 1996 for receiving from mobile stations suchas MS-2 1614.

During the UL sub-frame 1966, the frame structure 1952 for the RS-2 1620includes a UL MS zone 1921 for receiving from mobile stations such asMS-3 1616.

In the example of FIG. 19, each solid arrow 1960 as indicated in thelegend 1968 represents a transmission/reception using a portion of thefirst OFDM band “carrier 0”—⅓ in the particular example illustrated,each long dashed arrow 1962 as indicated in the legend 1868 representsthe transmission/reception using the second OFDM band “carrier 1”, andeach short dashed arrow 1964 as indicated in the legend 1868 representsthe transmission/reception using the third OFDM band “carrier 2”. In theexample illustrated, the partial band signals are used to transmit toand from mobile stations; thus, for BS 1610, RS-1 1618 and RS-2 1620,each are simultaneously allocated a third of the OFDM band during the DLsub-frame 1965 for transmission to MSs. Similarly, for BS 1610, RS-11618 and RS-2 1620, each are simultaneously allocated a third of thefirst OFDM band during the UL sub-frame for reception from MSs. Theentire second OFDM band is used for transmission/reception between theBS and the first tire RS (RS-1 1618), and the entire third OFDM band isused for transmission/reception between first and second tier RSs (RS-11618 and RS-2 1620). For the particular example illustrated, two radiosare provided in the first tier RS to allow the reception from the BS oncarrier 1 simultaneously with the transmission to the second tier RSs oncarrier 2.

The embodiments described above, and the specific examples thereof shownin FIGS. 16 to 19 all assume a TDD separation between DL and ULtransmissions. Further embodiments are provided that parallel theembodiments described with the exception that the separation between DLand UL transmission uses FDD. All of the examples described above alsocan be modified to this context; the only difference is that rather thanhaving UL sub-frames and DL sub-frames that are transmitted duringseparate time intervals, UL frames and DL frames are simultaneouslytransmitted, but on different frequencies.

RS_Preamble

In systems that do not use relay stations, the BS transmits a preamblethat is used by mobile stations to measure radio propagation environmentand enable MS cell selection. In 802.16e, this preamble is transmittedat the start of every DL sub-frame. When relay stations are present,they also transmit such a preamble in a similar manner so that MS cellselection can be performed as before. This preamble is referred to as a“normal preamble”. A problem with this approach is that an RS needs tobe able to look at a received preamble and transmit a preamble at thesame time. An embodiment of the invention provides a method of apreamble transmission by the RS that enables RS radio environmentmeasurement without interrupting MS cell selection.

In a particular implementation, a new preamble, referred to as anRS_preamble since it is transmitted by the RS only and not the BS, istransmitted in every Nth frame, where N≧1, once the RS enters thenetwork. In some embodiments, the RS_preamble is transmitted in additionto the normal preamble. In some embodiments, frames are as defined in802.16e, but other frame definitions are contemplated.

In some embodiments, the RS_preamble is transmitted within a ULsub-frame for TDD implementations or a UL sub-frame for FDDimplementations. Note this is in contrast to the normal preamble that istransmitted during the DL sub-frame. A pseudo-random noise (PN) sequencefor each respective RS preamble may be the same as that of an assignednormal preamble or the PN sequence may be different.

The RS's transmission and receiving of this RS_preamble is synchronizedso that at each RS_preamble transmission time, RSs that need to listento preambles are not transmitting preambles at the same time as they arereceiving the preambles. For example, first tier RSs can simultaneouslytransmit their preambles during a first preamble transmission period,and second tier RSs can monitor these; similarly, second tier RSs cansimultaneously transmit their preambles during a second preambletransmission period, and first and/or third tier RSs when present canmonitor these. In a particular example, first tier RSs transmit theirpreamble during odd UL sub-frames or UL frames, and second tier RSstransmit their RS_preamble during even UL sub-frames or UL frames.

In some embodiments RS_preamble reuse within a cell is employed.

In some embodiments, for the multiple carrier case such as the exampleof FIG. 19, a common channel is defined as a primary channel fortransmitting an RS_preamble for each respective RS to determine a radioenvironment measurement. The radio environment measurements are used to,for example establish topology, transmit broadcast traffic and RSrelated control messages, and negotiate or declare the transmission andreceiving schedule on another channel.

Channel Coordination

Another embodiment of the invention provides a method of channelcoordination for an RS. A channel is defined as a zone on a carrier, andas in previous embodiments, there may be one or multiple carriers eachof which has a respective OFDM band.

Variables that affect channel coordination may include the number ofradios of an RS, a measurement of RS load, and an environmentmeasurement of an RS.

In a first example of an environment measurement by a RS, the RSmeasures a neighboring station's (other RSs and/or the BS) preamble orcommon synch channels after the network entry procedure. The measurementmay be synchronized within a cell and controlled by the BS to ensurethat at a given time a particular RS stops transmitting preamble/commonsynch and measures other neighboring station's preambles. When an RSmeasures the preamble of other respective RSs, it may not be able totransmit its own preamble. The RS may stop sending a preamble for oneframe. In some embodiments, if the RS stops sending preambles, before itstops sending preambles, it will notify MSs it is associated with sothat none of the MSs will initiate a handoff due to what the MSs wouldotherwise perceive as a signal drop based on the missing preamble.

In a second example of an environment measurement by an RS, theRS_preamble mechanism described previously is employed.

Centralized Channel Coordination by BS

In some embodiments, centralized channel coordination is performed bythe BS based on one or more of the above-mentioned variables. The RSreports its capability during network entry, for example a number ofradios, etc. The RS also reports its load statistics to the BS. This mayfor example occur periodically, on-demand or autonomously. In someembodiments, the RS periodically or on-demand measures signallingstrength and/or channel quality of neighboring RSs and reports thesemeasurements to the BS. The BS then determines the channel assignmentfor each RS and broadcasts this information to the involved RSs.

Distributed Channel Coordination

In some embodiments, distributed channel coordination is performed bythe BS based on the above-mentioned variables. For example, the BSdetermines the channel assignment for an RS that is one hop away fromthe BS using the same procedure as above for centralized channelcoordination. The RS then determines the channel assignment for an RSthat is one hop away from the RS. This process continues for subsequentRSs that are each one hop away from an RS determining the channelassignment.

Hybrid of Distributed and Centralized Channel Coordination

With this embodiment, the BS determines channel assignment for each RSin any of a first N hops, using the same approach as above forcentralized channel coordination, and the remaining channel assignmentsusing the distributed channel coordination approach. More specifically,relay stations that are M hops away, where M≧N, will perform channelassignment for relay stations that are M+1 hops away.

The following are a set of messages that can be introduced for achievingthe above-described embodiment:

a request message that includes a list of RS IDs (relay stationidentifications) from which the BS requests measurements made by RSs,for example an RS_ENV-REQ (relay station environment request) message;

a response message to the RS_ENV-REQ message sent by the RSs. For eachmeasured RS, the RS sends an RS ID (may be avoided if in the order of RSID) and the measurement information, for example RS_ENV-RSP (relaystation environment response));

an advertisement (ADV) message for broadcasting channel coordinationcontrol information by the BS to its RSs or by an RS to its next hopRSs, for example RS_Channel-ADV (relay station channel advertisement).For each next hop RS, excluding the end RS, which has no next hop RS,the BS or RS sends an RS ID, transmission OFDM symbol and carrier and/orpower, receiving OFDM symbol and carrier, and action time;a request message sent by the BS to the RS to request transmission OFDMsymbol and carrier and/or power information and receiving OFDM symboland carrier information, for example RS_Channel_REQ (relay stationchannel request);a response message sent by the RS to the BS in response to theRS_Channel_REQ, for example RS_Channel-RSP (relay station channelrequest).RS DL Resource Allocation Methods

The RS DL resource is a transmission resource used for communicationfrom the BS to the RS and from the RS to its next hop RS. In someembodiments, when an RS is forwarding traffic for multiple MSs(aggregated traffic), the aggregated traffic presents a less burstynature than traffic dedicated to a single MS. As such, the trafficpattern is similar to a connection-oriented connection. Furthermore,since most RSs may be fixed, a change in channel conditions from the BSto RS and RS to RS may be less frequent than that of a BS to MS or RS toMS, and the channel may remain unchanged for a duration that is longerthan a duration of a frame, for example a frame duration defined by802.16e. Because of these distinctions, a resource assignment mechanismcan be different from that currently supported by 802.16e for MS.

In some implementations, a persistent DL RS related resource assignmentmechanism is employed. With such a mechanism, a BS or an RS can assign aDL resource to its descendent RS for a period of time longer than aframe, a frame being the nominal period for assignment, for exampleaccording to current 802.16e specifications. The resource assignment canbe updated from time to time. Variables of the resource assignmentinclude for example any one or more of resource size, resource locationand MCS (modulation and coding scheme). In some embodiments, theresource assignment can be supplemented beyond an existing persistentresource assignment from time to time. The resource can also beterminated when appropriate, such as when the resource is no longerneeded.

In some embodiments, the RS is assigned a dedicated feedback channel fora period of time. The feedback channel may be present every N frameswhere N is a number greater than or equal to than one. The feedbackchannel can be used for various purposes. For example, the RS may usethis feedback channel to send a channel quality indicator, a feedbackheader or a BW (bandwidth) request periodically.

The following type of messaging can be employed to implement the abovemethod, but other implementations are possible.

An assignment information element (IE) is introduced, which could beplaced in an 802.16e UL-MAP or in an RS-MAP according to embodiments ofthe present invention. An information element is a portion of thetransmission resource used to provide information to a station receivinga transmission on the transmission resource. For example, the DL andUL-MAP portions of the frame may include multiple different types ofIEs. The assignment IE may define four types of signalling. For example,a first type of signalling is “Full assignment” signalling, whichincludes information fields for RS ID (Relay station identification),Resource size and location, and MCS. The first type of signallingallocates a persistent UL resource defined by the contents of the “Fullassignment” signalling fields. A second type of signalling is“Supplementary” signalling, which includes information fields for RS IDand resource size and location. The second type of signalling allocatesan additional UL resource defined by the contents of the “Supplementary”signalling fields. A third type of signalling includes “Termination”signalling, which includes an information field for RS ID. The thirdtype of signalling terminates a UL resource for the RS defined in the“Termination” signalling field. A fourth type of signalling is “Update”signalling, which includes information fields for one or more of: Updatesize (defines a new size), Update position (defines a new position) andUpdate MCS (defines a new MCS). The fourth type of signalling updates aUL resource defined by the parameters in the contents of the “Update”signalling fields. The assignment IE in a given frame may include someor all of the fields defining the four types of signalling.

In some embodiments, the information fields in the assignment IE eachaccommodate a series of respective bits having a pre-determined length,which are implementation specific.

RS UL Resource Allocation Methods

Another embodiment of the invention provides a method of allocating atransmission resource used for communication from the RS to the BS andfrom an RS to its parent RS. In some embodiments, when the RS isforwarding traffic from multiple MS to BS (aggregated traffic), theaggregated traffic presents a less bursty nature than traffic dedicatedto a single MS. The traffic pattern is similar to a connection-orientedconnection. Since most of the RSs may be fixed, a change in the channelconditions from the RS to the BS and from the RS to its parent RS may beless frequent than that of a MS to BS or MS to RS. The channel mayremain unchanged for some time, for example longer than a frame asdefined by 802.16e. Because of this, the resource assignment mechanismcan be different from that currently supported by 802.16e for MS.

RS UL Resource Request

A first aspect of an RS resource allocation mechanism is a UL resourcerequest.

Non-Contention Based Approach

In some embodiments, UL resource requesting is performed using anon-contention based approach. For example, each RS is assigned adedicated UL resource for an RS to send a resource request message, suchas a MAC (media access control) header, every N frames, where N is apre-defined number. In some embodiments, the dedicated UL resource is achannel that may be the same as the feedback channel or a differentchannel. Various types of resource request MAC headers can be employedas a UL bandwidth request header. For example, a BW request header andother types of known feedback headers may be employed. A header definedas “RS-BW request header” is also provided herein.

A very specific example of the RS-BW request header is a header that isfour bytes in length and includes information fields for defining therequest type (Type), the bandwidth request, and a header check sequence(HCS). For example, in some embodiments, the “Type” field is 1 bit, theBandwidth request field is 22 bits and the HCS field is 8 bits. The 1bit “Type” field may indicate options such as “increased” and“aggregated” by the use of the single bit as either “0” or “1”. When the“Type” selected is “aggregated”, the request is made to replace aprevious connection bandwidth with a new requested amount. When the“Type” selected is “increased”, the request is made to increase acurrent bandwidth amount by the requested amount.

Contention Based Approach

In some embodiments, UL resource allocation requesting is performedusing a contention based approach. The RS uses a BW request rangingmethod to request a UL resource. This may for example involve the use ofeither an existing 802.16e BW request header or a “RS-BW requestheader”.

The following is a very specific example of the “RS-BW request header”,which has information fields to define a request type (Type), a stationidentification (Node ID), the bandwidth request and a HCS. For example,in some embodiments, the Type field is 1 bit, the Node ID is 8 bits, thebandwidth request field is 22 bits and the HCS field is 8 bits. The 1bit “Type” field may indicate options such as “increased” and“aggregated” by the use of the single bit as either “0” or “1”. When the“Type” selected is “aggregated”, the request is made to replace aprevious connection bandwidth with a new requested amount. When the“Type” selected is “increased”, the request is made to increase acurrent bandwidth amount by the requested amount.

RS UL Resource Grant

A second aspect of an RS resource allocation mechanism is a UL resourcegrant. In some embodiments, this is triggered by the reception of the ULrequest as described above. In some embodiments, the resource allocationis a persistent UL resource allocation with functionality for updating,supplementing and terminating in a similar manner as that for DLresource allocation, which is described above.

The following is an example of a set of messages that can be used toimplement the UL resource grant, but more generally any messagingprotocol can be employed.

An assignment IE is introduced, which could be placed in an 802.16eUL-MAP or in an RS-MAP according to embodiments of the presentinvention. The assignment IE may define four types of signalling. Forexample, a first type of signalling is “Full assignment” signallingwhich includes information fields for RS ID, Resource size and location,and MCS. A second type of signalling is “Supplementary” signalling whichincludes information fields for RS ID and resource size and location. Athird type of signalling is “Termination” signalling which includes aninformation field for RS ID. A fourth type of signalling is “Update”signalling which includes information fields for one more of: Updatesize (defines a new size), Update position (defines a new position) andUpdate MCS (defines a new MCS). The uses for the four types ofsignalling are the same as the uses for the corresponding types ofsignalling for DL resource allocation described above. The assignment IEin a given frame may include some or all of the fields defining the fourtypes of signalling.

MS UL Resource Allocation

Another embodiment of the invention provides a method of performing MSUL resource allocation. A MS UL resource is the resource used forcommunication from MS to BS or from a MS to an RS.

With the existing MS UL resource request supported by 802.16e, apiggyback request sub-header is employed. A piggyback request sub-headeris part of a MAC frame carrying user data rather than a separatebandwidth request management MAC frame. The piggyback request sub-headermay be encrypted, and is used along with data. A BW request header isalso used, either on a non-contention based UL resource, or on acontention based UL resource. Due to the encryption of the piggybackrequest sub-header, the associated RS may not be able to decrypt thesub-header, assuming that there is end-to-end privacy. Because of this,the request has to go to the BS first and the BS will inform the requestto the associated RS resulting in a long delay.

In some embodiments for MS UL resource requesting, the piggyback requestsub-header function is disabled when MS UL resource requesting is needed(for multi-hop away MS). An MS uses the BW request header transmittedalong with data, for example a data PDU (packet data unit), if there isa UL resource available. The RS associated with the MS understands theheader because no encryption is performed on the BW request header. Thepiggyback request sub-header can be disabled, for example through usedof a management message request and response, for example SBC-REQ/RESmessages.

In some embodiments for MS UL resource requesting, the piggybacksub-header is forwarded to the BS by an RS associated with the MS. TheBS decrypts the piggyback sub-header and informs the associated RS by amessage, for example an RS_MSBW-IND message. Delay can be reduced byusing a dedicated DL/UL RS resource assignment mechanism.

An example of a message that can be used to implement the second optionis the RS_MSBW-IND message. The RS_MSBW-IND message defines a connectionbetween the MS and BS, a connection between the MS and RS and includes abandwidth request. In a specific example of the RS_MSBW-IND message, themessage includes information fields to define a basic CID (connectionidentification) of the MS, the bandwidth request, and transport CID thatidentifies the connection path.

Intra-Cell Peer-to-Peer Communication

Another embodiment of the invention provides mechanisms for performingintra-cell peer-to-peer communication. This is to enable communicationbetween MSs or between RSs that are associated with the same BS. Thepeer-to-peer communication is peer-to-peer in the sense that packetsreceived from a MS do not need to go all the way up a hierarchy to anetwork gateway before being turned around and sent back to another MSand/or RS served by the same BS.

In this embodiment, a simple route function is introduced in aconvergence sub-layer. The convergence sub-layer is a layer above MAClayer (layer 2), but below the physical layer (layer 1) as defined inthe OSI open system interconnection model.

A destination address table is maintained by the BS that includesdestination addresses that are served by the BS. The table is updated atone or more of the following times: after a MS enters the network; at aMS hand off when the MS is leaves the cell being served by the BS; andat a MS hand off when the MS is enters the cell being served by this BS.

Upon receiving a SDU (service data unit) (more generally anytransmission) from the UL, a destination address of the SDU isdetermined. A SDU is a data format utilized in 802.16 MAC layer. If thedestination address is within the table, the SDU is routed to a DLconvergence sub-layer; otherwise the SDU is routed to an upper layer,for example through SAP (service advertising protocol).

A detailed block diagram of a convergence sub-layer function example isprovided in FIG. 33. In the left-hand portion of the figure a packet isreceived from an MS or associated RS 3310. The packet is reconstructedat 3320, and then subject to destination address filtering at 3330 withthe table that includes all addresses covered by the BS. If the addressis not present, the packet is passed on to the SAP, and then on to anupper layer entity at 3340. If the address is present, the packet ispassed over to the DL convergence sub-layer at 3350, this being thefunctionality shown in the right hand side of the figure.

In the DL convergence sub-layer, a packet is received that is destinedto another address that is served by that BS. DL classification and CIDmapping is performed at 3360, and the packet is transmitted to anotherMS or associated RS at 3370.

A similar concept can be applicable to RSs.

Referring to FIG. 20, shown is a specific frame structure for handlingthe presence of relays in an OFDM communication system. FIG. 20 alsoincludes the example network 1600 of FIG. 16 to clearly illustrate thecorrespondence of the frame structure to the BS and relay stations RS-1and RS-2. In FIG. 20, the horizontal direction of the frame structure istime, representing multiple OFDM symbols, while the vertical directionis frequency, representing multiple OFDM sub-carriers. In the first row2030, communication from the perspective of BS 1610 is shown; in thesecond row 2035, communication from the perspective of a first tierrelay station RS-1 1618 is shown; in the third row 2040, communicationfrom the perspective of a second tier relay station RS-2 1620 is shown.In the time direction, frames are defined, each consisting of multipleOFDM symbols.

In the embodiment illustrated in FIG. 20, an DL/UL (downlink/uplink)duplex structure is employed. Each frame 2050,2052,2054,2056 includes aDL sub-frame 2024,2026 used for DL communication and a UL sub-frame2025,2027 used for UL communication. The size of these sub-frames can bestatically or dynamically defined. The format of FIG. 20 is slightlydifferent from the format of FIGS. 18 and 19 in that both sides of acommunication are shown. More specifically, a portion of a frame used totransmit from a first entity, for example BS 1610, to a second entity,for example RS-1 1618, is shown in both the frame structure 2030 for BS1610 and the frame structure 2035 for RS-1 1618.

The frames are divided into first and second groups of frames. In theillustrated example, the first group is the odd frames 2050,2054 and thesecond group is the even frames 2052,2056 but other definitions arepossible. In FIG. 20, the first group of frames is used for UL and DLcommunication between BS 1610 and its first tier RSs (RSs one-hop awayfrom BS), for example RS-1 1618 and for communications (not shown)between the BS 1610 and MS directly served by the BS, for example MS-11612.

In addition, in some embodiments, the first group of frames is also usedfor communication between the second tier RSs (two-hops away from theBS), for example RS-2 1620, and MS associated with the second tier RSs,for example MS-3 1616. This assumes interference from transmissions fromthe BS will not significantly effect transmissions from second tier RSs.

In FIG. 20, the second group of frames 2052,2056 is used for UL and DLcommunication between the first tier RS RS-1 1618 and any RS/MS it iscommunicating with. This would include communications between RS-1 andRS-2 1620, and include communications between RS-1 and MS-2 1614 (notshown).

In some embodiments, the BS 1610 is also permitted to communicate duringthe second group of frames with mobile stations at a reduced power, forexample with mobile stations that are closer to the base station, so asnot to interfere with the relay communications.

In some embodiments, in order to ensure backwards compatibility with MSthat support 802.16e, each RS, after network entry, transmits a preamble2060 and a FCH 2062 on every frame as shown.

In some embodiments, having defined the first and second groups offrames, RS_Zones are defined in the time domain to enable more efficientsub-channelization. More specifically, a DL RS_Zone is defined fordownlink transmission (from a base station or a relay to another relay)and a UL RS_Zone is defined for uplink transmission (from a relay toanother relay, or from a relay to BS. Remaining resources are availablefor communication with mobile stations.

In the illustrated example, four TDD frames 2050,2052,2054,2056 areshown. Only TDD frames 2050 and 2052 will be described in detail. TDDframe 2050 is composed of a DL sub-frame 2024 during which downlinktransmissions from the BS occur and a UL sub-frame 2025 during whichuplink transmissions to the BS occur. Similarly, TDD frame 2052 iscomposed of a DL sub-frame 2026 during which downlink transmissions fromfirst tier RS occur and a UL sub-frame 2027 during which uplinktransmissions to second tier RS occur. A legend indicating differingshadings for the differing zone types is generally indicated at 2068.

During the DL sub-frame 2024, the frame structure 2030 for the BS 1610includes a preamble 2064 and FCH 2065. In some embodiments, the FCH isconsistent with 802.16e. The frame structure 2030 includes a DL-RS zone2076 that includes an R-MAP 2074 for transmission to relay stations suchas RS-1 1618. The frame structure 2030 may also include a DL_MS zone(not shown) for transmission directly to mobile stations such as MS-11612.

During the DL sub-frame 2024, the frame structure 2035 for the RS-1 1618includes a preamble 2062 and FCH 2065. In the illustrated example, anarea of the DL sub-frame 2024 in frame structure 2035 is shown forreceiving the DL-RS zone 2076 that includes the R-MAP 2074. The framestructure 2035 may include a DL_MS zone (not shown) for transmissiondirectly to mobile stations such as MS-2 1614 as well as RS radioswitching periods (not shown). During the radio switching periods, theRS switches its radio from transmitting to receiving or vice versa.

During the DL sub-frame 2024, the frame structure 2040 for the RS-2 1620includes a preamble 2060 and FCH 2062. The frame structure 2040 mayinclude a DL_MS zone (not shown) for transmission directly to mobilestations such as MS-3 1616. There may also be RS radio switchingperiods.

During the UL sub-frame 2025, the frame structure 2030 for the BS 1610includes an area of the DL sub-frame 2024 for receiving UL RS zone 2078transmissions from relay stations such as RS-1 1618. The frame structure2030 may also include a UL MS zone (not shown) for receiving from mobilestations such as MS-1 1612.

During the UL sub-frame 2025, the frame structure 2035 for the RS-1 1618includes the UL RS zone 2078 for transmission from relay stations suchas RS-2 1620. The frame structure 2035 may also include a UL MS zone(not shown) for receiving from mobile stations such as MS-2 1614. Theremay also be RS radio switching periods.

During the UL sub-frame 2025, the frame structure 2040 for the RS-2 1620may include a UL MS zone (not shown) for receiving from mobile stationssuch as MS-3 1616.

During the DL sub-frame 2026, the frame structure 2030 for the BS 1610includes a preamble 2064 and FCH 2065. The frame structure 2030 may alsoinclude a DL_MS zone (not shown) for transmission directly to mobilestations such as MS-1 1612.

During the DL sub-frame 2026, the frame structure 2035 for the RS-1 1618includes a preamble 2060 and FCH 2062. The frame structure 2035 includesa DL-RS zone 2080 that includes an R-MAP 2082 for transmission to relaystations such as RS-2 1620. The frame structure 2035 may include a DL_MSzone (not shown) for transmission directly to mobile stations such asMS-2 1614 as well as RS radio switching periods.

During the DL sub-frame 2026, the frame structure 2040 for the RS-2 1620includes a preamble 2060 and FCH 2062. In the illustrated example, anarea of the DL sub-frame 2026 in frame structure 2035 is shown forreceiving the DL-RS zone 2080 that includes the R-MAP 2082. The framestructure 2040 may include a DL_MS zone (not shown) for transmissiondirectly to mobile stations such as MS-3 1616. There may also be RSradio switching periods.

During the UL sub-frame 2027, the frame structure 2030 for the BS 1610may include UL MS zone (not shown) for receiving from mobile stationssuch as MS-1 1612.

During the UL sub-frame 2027, the frame structure 2035 for the RS-1 1618includes an area of the UL sub-frame 2027 for receiving a UL RS zone2094 from relay stations such as RS-2 1620. The frame structure 2035 mayalso include UL MS zone (not shown) for receiving from mobile stationssuch as MS-2 1614. There may also be RS radio switching periods.

During the UL sub-frame 2027, the frame structure 2040 for the RS-2 1620includes a UL RS zone for transmitting to relay stations, such as RS-11618. The frame structure 2040 may also include a UL MS zone (not shown)for receiving from mobile stations such as MS-3 1616.

Corresponding zones for transmitting/receiving are defined in the firstframe 2050 for the first tier RS RS-1 1618 and the BS 1610 in framestructures 2030,2035. During this time, the second tier relay RS-2 1620is only communicating with MS, for example MS-3 1616, so no zones aredefined. Similar zones are defined for communication between RS-1 1618and RS-2 1620 during each of the second group of frames 1652, includingthe second and fourth frames 2052,2056 in frame structures 2035,2040.

The size of the RS_Zone and a starting OFDM symbol within a frame can bedefined for example by a) a fixed size, b) slowly changed in sizethrough use of a management MAC message, and c) dynamically changed insize and forecast by BS and DL transmitting RSs a few frames before thechange.

In some embodiments, an RS-MAP is transmitted to indicate the resourceassignments for the DL RS_zone and/or the UL RS_zone. These resourceassignments indicate how the contents of the transmissions are assignedto particular mobile stations. The RS-MAP, if needed, can be transmittedby each DL transmitting BS and RS in corresponding DL transmittingframes.

An RS-MAP resource allocation includes one or more of resource locationinformation, resource size information and modulation and code scheme(MCS) information. Location information may be provided in the form of afixed offset relative to the beginning of a frame or a fixed offsetrelative to the RS_Zone. Size information can for example be provided bymodifying the 802.16e OFDMA downlink Frame Prefix Format by changing thelast four reserved bits into “RS-MAP length (units in 4 bytes)”. MCSinformation can for example be provided by either of two options whichinclude a) slowly updating the MCS based on worst link budgets among allattached RS and b) multicasting the MCS information to the correspondingRSs when needed.

As an alternative to transmitting the RS-MAP, the allocations for the RSmay be included together with allocations for non-relay stations in asingle MAP.

Multiple RS-MAPS may be sent with each respective RS-MAP includingresource assignments for one or more RS sharing similar channelqualities.

DL Preamble Transmission

In some embodiments, DL preambles are used to transmit PN codes in amanner consistent with current 802.16e definitions. These provide for atotal of 114 PN sequences (57×2) and 32 IDcell definitions. In someembodiments, each transmitting station (BS and RS) is physicallydifferentiated within a geographic area by a respective distinctpreamble PN sequence for switching purposes. Each respective preamble PNsequence implies a particular IDcell. Thus, each RS is assigned adedicated PN sequence. This enables a preamble sequence space reuse thatis larger than what 802.16e defines. The preamble can be transmittedwithin the network synchronized in a manner to enable serving stationselection.

In some embodiments, the 802.16e standard is adapted to be used in thismanner by modifying REG-REQ/RSP (registration request/response) messagesto be used by the relay station when it enters the network. For example,the REG-REQ/RSP messages can be modified to include an assigned PN indexinformation field, a DL_PermBase information field, and a PRBS_IDinformation field. DL_PermBase and PRBS_ID are index numbers used fordata randomizations in the 802.16e standard. They are essentially linkedto the Base station ID to ensure that each base station randomizes datain different manner. Specifically, DL_PermBase is used in relation tophysical sub-channel to logical sub-channel mapping and PRBS_ID is usedin relation to data scrambling.

In some embodiments, an algorithm is employed to perform PN indexselection. The algorithm selects and assigns to an RS the PN indexselection to minimize IDcell collision. The algorithm also may assignDL_PermBase and PRBS_ID values.

For the purpose of routing, a station (BS and RS) is identified by a BSID (base station identification) in a MAC management message. For thispurpose, each RS is assigned a BS ID (48 bits). In some embodiments, the802.16e standard is adapted to be used in this manner by modifying theREG-REQ/RSP to include the assigned BS ID.

Various options exist for PN assignment for a mobile relay station (MRS)preamble. In some embodiments, the preamble PN index does not changeduring handover of an MRS from a BS serving first cell to a BS serving asecond cell as the MRS moves between the first and second cells. Thisinvolves defining a system reserved for a sub-set of PN indexes for theMRS so as to avoid collision when the MRS moves across the network. Insome embodiments, the preamble is changed or re-assigned duringhandover, and no PN needs to be reserved for the MRS. In this case, theMSs associated with the MRS need to be informed of the change or theymust perform re-synchronization. In a particular example, this isachieved by modifying a message, such as a mobile handoff messageresponse (MOB_MSHO_RSP) to include a preamble PN index.

TDM Channelization

A first example of DL Resource Multiplexing between BS/RS and RS andbetween BS/RS and MS employs the above-introduced DL RS_Zone for thetransmission from BS/RS to RS. The DL RS_Zone concept is illustrated inFIG. 21. In FIG. 21, a frame 2110 is a two dimensional channel resourcein which one dimension is represented by logical sub-channels and theother dimension is represented by OFDM symbols. The frame 2110 includesa DL sub-frame 2120 and a UL sub-frame 2130. In the DL sub-frame 2120there is a preamble 2140 and a FCH 2145. The DL RS_Zone 2150 is alsoincluded in the DL sub-frame 2120. This enables the definition ofsub-channel types with larger resource granularity and therefore lessassignment overhead. In some embodiments, the DL RS_Zone 2150 isconsistent with the DL RS_Zone described above with regard to FIGS. 16to 19.

A DL RS_Zone can, for example, be defined to include one or multipleOFDM symbol(s) within a corresponding DL sub-frame or to include anentire DL sub-frame.

Having defined the DL RS_Zone, sub-channelization can be performed toprovide assignment granularity. In some embodiments, a bin conceptsimilar to that used for 802.16e AMC (adaptive modulation and coding)sub-channelization is employed to define a building block forsub-channelization of the DL RS_Zone. A bin is defined as a group ofcontiguous sub-carriers (G) in one OFDM symbol. Sub-carriers in a binindexed as k are re-indexed as sub-carrier(k,i)=sub-carrier Gk+i (i=0,1, . . . , G−1). Each bin includes pilot sub-carriers.

The following is a specific example of how the bin concept can beimplemented, but other examples are possible. For one antenna, asub-carrier indexed with a floor(G/2) is reserved as a pilotsub-carrier. The term “floor” is being used as a mathematical functionfor rounding a real number to a largest integer less than or equal tothe real number. For two antennas, two sub-carriers indexed withfloor(G/2) and floor(G/2)+1 respectively, are reserved as pilotsub-carriers, one pilot sub-carrier for each antenna. For four antennas,four sub-carriers indexed with floor(G/2), floor(G/2)−1, floor(G/2)+1and floor(G/2)+2 respectively, are reserved as pilot sub-carriers, onepilot sub-carrier for each antenna.

Examples of bin construction for even and odd bin sizes for one and twoantennas are provided in FIG. 22. Each of the examples depicts a singlecolumn of rectangular boxes in which the column represents the bin andeach box represents a sub-carrier in the bin. Bin constructions for usein single antenna implementations are illustrated at 2210 and 2220. Abin with G=12 including a pilot in the sixth sub-carrier 2215 isillustrated at 2210. A bin with G=9 including a pilot in the fifthsub-carrier 2225 is illustrated at 2220. Bin constructions for use intwo antenna implementations are illustrated at 2230 and 2240. A bin withG=12 including a pilot for a first antenna in the sixth sub-carrier 2233and a pilot for a second antenna in the seventh antenna 2235 isillustrated at 2230. A bin with G=9 including a pilot for a firstantenna in the fifth sub-carrier 2243 and a pilot for a second antennain the sixth antenna 2245 is illustrated at 2240.

The bins thus defined can then be used to define sub-channels to allowfor DL resource multiplexing. Sub-channelization can be defined by amatrix of N×M bins, in which N is a number of contiguous bins within anOFDM symbol and M as a number of consecutive OFDM symbols. The followingare specific examples of sub-channel types that might be provided: 1×12;1× size of RS_Zone (size of RS_Zone=number of OFDM symbols of RS_Zone);2×6; 2×12; 2× size of RS_Zone; 3×6; 3×12; 3× size of RS_Zone; 4×6; 4×12;4× size of RS_Zone; 6×6; 6×12; 6× size of RS_Zone. More generally, thesize of the sub-channel is implementation specific and can be a sizeother than the particular example described above.

FIG. 23 contains examples of two specific sub-channel definitions.Individual bins are identified by a single cross hatched elementindicated at 2030. A sub-channel including multiple bins is identifiedby a thick outline around the multiple bins, as indicated at 2040. A “1×size of RS_Zone” type sub-channel is indicated at 2315 in which thesub-channel is a single row of bins equal to the length of the DLRS_Zone. A “2×6” type sub-channel is indicated at 2325 in which thesub-channel is a matrix that is two rows of six bins. The DL RS_Zones2310 and 2320 include an implementation specific number of suchsub-channels.

FDM Channelization

In another embodiment, DL Resource Multiplexing between BS/RS and RS andBS/RS and MS is employed on an FDM (frequency division multiplexing)basis. This is particularly applicable in PUSC based systems. Forexample, in 802.16e, all available sub-carriers used for pilots and datain an OFDM symbol are divided into a set (for example six) of majorgroups and typically two of these major groups are assigned to eachsector of a multi-sector transmitter. In another embodiment, arespective fractional number of major groups such as these are dedicatedto BS/RS to RS transmission.

In some embodiments, a method employed for sub-channelization is thatwhich is defined in 802.16e, which is hereby incorporated by referencein its entirety. This is a distributed type of channel on the basis ofthe sub-carriers.

In some embodiments, a sub-channel is defined so as to enlargesub-channel size. This is a similar concept to the above-describedbin-based sub-channelization, but in which the bin is replaced by acluster. In some embodiments, clusters of a given sub-channel are notcontiguous. In some embodiments, a cluster is a group of bins. As theclusters of a given sub-channel do not need to be contiguous, adiversity type of sub-channelization is allowable on the basis ofclusters to be defined.

For UL Resource Multiplexing between RS and BS/RS and between MS andBS/RS, the above-introduced UL RS_Zone can be employed, as depicted inFIG. 24 by way of example. In FIG. 24, a frame 2410 is a two dimensionalchannel resource in which one dimension is represented by logicalsub-channels and the other dimension is represented by OFDM symbols. Theframe 2410 includes a DL sub-frame 2420 and a UL sub-frame 2430. In theDL sub-frame 2420 there is a preamble 2440 and a FCH 2445. The ULRS_Zone 2450 is also included as a portion of the UL sub-frame 2430. TheUL RS_Zone is used for the transmission from RS to BS/RS and enables thedefinition of new types of sub-channels. The new types of sub-channelsmay for example reduce the pilot overhead for fixed or low mobile RSand/or allow for larger resource granularity thereby achieving lessassignment overhead. In some embodiments, the UL RS_Zone is consistentwith embodiments described above with regard to FIGS. 16 to 19.

The UL RS_Zone definition can for example include one or multiple OFDMsymbol(s) within corresponding UL sub-frames, or may include an entireUL sub-frame.

The UL RS_Zone sub-channelization can for example be based on theenhancement of current 802.16e channelization using bin definitions.

A UL bin definition is defined as a group of contiguous sub-carriers (G)in one OFDM symbol. Sub-carriers in a bin indexed as k are re-indexed assub-carrier(k,i)=sub-carrier Gk+i (i=0, 1, . . . , G−1).Bin_without_pilot is defined as a bin where all sub-carriers are usedfor data; Bin_with_pilot is defined to include pilots. In someembodiments, transmissions include sets of bins some of which containpilots and others of which do not to reduce overhead. An example of abin_with_pilot definition for one antenna is a bin where one sub-carrieris indexed with a floor(G/2) reserved as a pilot sub-carrier. An exampleof a bin_with_pilot definition for two antennas is a bin where twosub-carriers are indexed with floor(G/2) and floor(G/2)+1 reserved aspilot sub-carriers. For example, a first antenna transmits a pilot atindex floor(G/2) and a null symbol location at index floor(G/2)+1 and asecond antenna transmits a pilot at index floor(G/2)+1 and a null symbollocation at index floor(G/2). More generally, in some embodiments, afirst bin definition includes pilot symbols, and a second bin definitiondoes not include pilot symbols, and a combination of the two bindefinitions is used for a given sub-channel.

FIG. 25 shows specific examples of bin definitions for two different binsizes and for bins with and without pilots. Each of the examples depictsa single column of rectangular boxes in which the column represents thebin and each box represents a sub-carrier in the bin. A bin for G=8including a pilot in the fourth sub-carrier 2515 is illustrated at 2510.A bin for G=8 without a pilot is illustrated at 2520. A bin for G=9including a pilot in the fifth sub-carrier 2535 is illustrated at 2530.A bin for G=9 without a pilot is illustrated at 2540.

Having defined a bin as a basic unit of channelization, sub-channels canbe defined similar to how it was done for downlink channelization.Specific examples in FIG. 26 illustrate a given type of sub-channel (M,which is a number of OFDM symbols in the sub-channel is known in whichall bins are “bin_without_pilot” bins, except the bins in an OFDM symbolindexed with floor [M/2]. Other breakdowns between bins with pilots andwithout pilots can be employed. In the illustrated example of FIG. 26,individual “bin_without_pilot” bins are identified by a single crosshatched element as indicated at 2630 and “bin_with_pilot” bins areidentified by a single solid black element as indicated by 2640. Asub-channel including multiple bins is identified by a thick outlinearound the multiple bins as indicated by 2650. A “1× size of RS_Zone”type sub-channel is indicated at 2615 in which the sub-channel is asingle row of bins equal to the length of the DL RS_Zone. A “2×6” typesub-channel is indicated at 2325 in which the sub-channel is a matrixthat is two rows of six bins. The DL RS_Zones 2310 and 2320 include animplementation specific number of such sub-channels.

In some embodiments, UL Resource Multiplexing between RS and BS/RS andMS and BS/RS is performed using FDM, which is particularly appropriatefor PUSC and/or optional PUSC. In some embodiments, a tile structure asdefined in 802.16e is employed. In some embodiments, a new tilestructure RS_tile is defined. A UL tile can be defined as an N×Mstructure in which N is the number of contiguous sub-carriers within anOFDM symbol and M is the number of OFDM symbols. Some examples of tilesare defined above in FIGS. 10-15.

In a particular example, an RS_tile type 24×3 is defined. Additionalstructure types include those having a size of 24×6, 24×12 and 24× sizeof UL RS_Zone. More generally, the size of the RS_tile is implementationspecific and can be a size other than the particular example describedabove.

In some embodiments, pilot transmission in a tile is performed with apilot sub-carrier density in RS_tile that is the same as current802.16e. In some embodiments, part of those sub-carriers are used fortransmitting pilots, and part of those sub-carriers are used forsounding. A specific example of this is shown in FIG. 27. Pilot pattern2710 is an example of a UL OPUSC pilot pattern having a basic tilestructure similar to that of 1310 in FIG. 13A including pilotsub-carriers (indicated by 2740 in legend 2730) in a first row of 3sub-carrier by 3 OFDM symbol tiles and sub-carriers used for sounding(indicated by 2750 in legend 2730) in a second row of 3 sub-carrier by 3OFDM symbol tiles. In other embodiments, a pilot density lower than thatof the current 802.16e tile is employed. Pilot pattern 2720 is anexample of a UL OPUSC pilot pattern having a similar tile structure to2710 including pilot sub-carriers in a first row of 3 sub-carrier by 3OFDM symbol tiles and no pilot sub-carriers.

In another embodiment, the entire frame resource is initially assumed tobe available for use for RS related transmission (DL/UL). RSsub-channels (RS_sub-channel) can be defined using any appropriatemethod including but not limited to those described above. In someembodiments, the resource used for MSs is assigned first using 802.16esub-channels and RS related resources are assigned later using RSsub-channels. All resources occupied by MSs will be punctured out, orremoved from the sub-channels to allow for the assigned resource for RS.This avoids hard partitioning between RS related resource and MS relatedresource.

RS 802.16e Preamble Transmission

In some embodiments, each RS is configured to transmit a preamble tofacilitate a MS to perform cell selection and handoff, as well as topotentially aid in other functionality. A specific example of such apreamble is that specified by 802.16e, but others may be used. In theexample that follows, 802.16e preambles are assumed, but similarpreamble re-use can be applied to any finite preamble resource. Withpreambles based on 802.16e-2005, there are a total of 114 preambles(identified by preamble as characterized by IDcell, segment and PNsequence) for 1024 mode and 512 mode. This preamble resource pool isshared between base stations and the RSs which are configured totransmit 802.16e preamble.

Preamble Selection

During RS initial network entry, an RS performs the cell selection in asimilar manner that a MS does. In some embodiments, this procedure isenhanced to enable the RS assistance in preamble PN sequence selection.

To begin, the RS maintains information identifying a set of possiblepreambles for use in the system to be measured. In an example approachto achieving this, the relay station maintains preamble informationconsisting for example of an entry for each preamble with each entryhaving a preamble index corresponding to the PN sequence. The RSmeasures the strength of each of the possible preambles and records thestrength of each. The strength of each preamble may be recorded in atable for the corresponding entry. The longer the time taken for thismeasurement, the more the impact of fading will be minimized. When themeasurement procedure is finished, for example when some number offrames has been measured, the RS determines its serving station (a basestation or possibly another relay station) based on these measurements.The particular criteria here are not relevant and any method of cellselection can be employed.

Having performed cell selection, preamble selection is performed toselect the preamble that will be transmitted by the relay station. Insome embodiments, the RS uses the strength information to determine acandidate preamble pool for the purpose of a preamble selection. In someembodiments, the candidate preambles in the candidate pool are thosepreambles whose strengths measured by this RS are lower than apre-defined threshold. More complicated selection procedures are alsocontemplated; for example any preamble below a first threshold up tosome number and any preamble below a second threshold up to some numberand so on; the lowest N below a particular threshold, etc. The RS thenselects one preamble from the candidate pool and reports this back toits serving base station, either directly or via other relay stations.More generally, the RS may select some number M of preambles andindicate these to its serving base station. The selected preambles canbe indicated by the preamble index. The base station may agree or deny asingle selected preamble. In some implementations, the base stationsignals a determination of one or more preambles to the relay station.In some embodiments, multiple preambles are selected by the relaystation, and the base station signals a selection of one of these.

In some embodiments, preamble selection is cooperative in that both therelay station and the base station participate. To begin, the RS reportspreamble measurement information to its BS. This may for example containa list that includes all the preamble indexes whose strength measured bythe RS are higher and/or lower than a pre-defined threshold, but otherinformation may alternatively be fed back to the BS.

The BS assigns a preamble based on the information from the listreported by this RS, for example by selecting one on the list or one noton the list depending on what is fed back. In some embodiments, the BStakes into account other available information such as what preamble(s)are currently in use within the cell and in use in neighboring cell(s),assuming this information is made available by neighbor BSs. Suchinformation may be made available for example through backhaulconnections.

Advantageously, by reasonable setting of threshold and measurement time,preamble collision (multiple devices attempting to use the same preamblein an overlapping coverage region) can be reduced, and the need for acomplex preamble plan can be avoided.

In an example implementation, a Config-REQ/RSP MAC management messageutilized. In the Config-REQ/RSP MAC management message the 4 bitreserved field is replaced with “RS_Zone Prefix location” The “RS_ZonePrefix location” indicate the OFDM symbol index relative to thebeginning of current frame in units of 2 OFDM symbols.

In some embodiments, preamble strength measurement information, madeavailable by mobile stations and/or relay stations is used by the basestation to perform resource re-allocation. To begin, mobile stationsreport the strengths of preambles transmitted by relays, and moregenerally the strength of all the preambles that it can measure. In someembodiments, a mobile station may not necessarily distinguish between apreamble transmitted by a BS and a preamble transmitted by an RS andreports the signal strength of both. However, when a BS receives thesignal strength measurements it knows which measurement is for the BSpreamble and which measurement is for the RS preamble. The BS then usesthis information to intelligently perform resource re-use between therelay stations. For example, when a MS reports negligible strength of apreamble transmitted by a one RS and good signal strength from a secondRS, the signals transmitted by that first and second RSs may notinterfere with each other and as such resources that are in use by theneighbouring base station. Examples of resources that can be allocatedin this manner include resources within OFDM frames—for exampleparticular sub-carriers over particular OFDM symbols or frames.

In a specific example of performing resource re-use based on thestrength measurements, if a first MS reports a good signal strength froma first RS and poor signal strength from a second RS, and a second MSreports a good signal strength from the second RS and poor signalstrength from the first RS, then the same or at least partiallyoverlapping resources, can be assigned at the first and second RS fortransmitting to the first and second MS with the understanding that thiswill not result in interference.

More generally, resources can be allocated at a first relay station tothe mobile station that are also being allocated at a second relaystation whose preamble signal strength measurement is s below a definedthreshold.

Description of Example BS and MS

For the purpose of providing context for embodiments of the inventionfor use in a communication system, FIG. 28 shows a base stationcontroller (BSC) 10 which controls wireless communications withinmultiple cells 12, which cells are served by corresponding base stations(BS) 14. In general, each base station 14 facilitates communicationsusing OFDM with mobile and/or wireless terminals 16, which are withinthe cell 12 associated with the corresponding base station 14. Themovement of the mobile terminals 16 in relation to the base stations 14results in significant fluctuation in channel conditions. Asillustrated, the base stations 14 and mobile terminals 16 may includemultiple antennas to provide spatial diversity for communications. Alsoshown are relay stations 17.

A high level overview of the mobile terminals 16 and base stations 14upon which aspects of the present invention are implemented is providedprior to delving into the structural and functional details of thepreferred embodiments. With reference to FIG. 29, a base station 14 isillustrated. The base station 14 generally includes a control system 20,a baseband processor 22, transmit circuitry 24, receive circuitry 26,multiple antennas 28, and a network interface 30. The receive circuitry26 receives radio frequency signals bearing information from one or moreremote transmitters provided by mobile terminals 16 (illustrated in FIG.28). A low noise amplifier and a filter (not shown) may co-operate toamplify and remove broadband interference from the signal forprocessing. Downconversion and digitization circuitry (not shown) willthen downconvert the filtered, received signal to an intermediate orbaseband frequency signal, which is then digitized into one or moredigital streams.

The baseband processor 22 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 22 is generallyimplemented in one or more digital signal processors (DSPs) orapplication-specific integrated circuits (ASICs). The receivedinformation is then sent across a wireless network via the networkinterface 30 or transmitted to another mobile terminal 16 serviced bythe base station 14.

On the transmit side, the baseband processor 22 receives digitized data,which may represent voice, data, or control information, from thenetwork interface 30 under the control of control system 20, and encodesthe data for transmission. The encoded data is output to the transmitcircuitry 24, where it is modulated by a carrier signal having a desiredtransmit frequency or frequencies. A power amplifier (not shown) willamplify the modulated carrier signal to a level appropriate fortransmission, and deliver the modulated carrier signal to the antennas28 through a matching network (not shown). Various modulation andprocessing techniques available to those skilled in the art are used forsignal transmission between the base station and the mobile terminal.

With reference to FIG. 30, a mobile terminal 16 configured according toone embodiment of the present invention is illustrated. Similarly to thebase station 14, the mobile terminal 16 will include a control system32, a baseband processor 34, transmit circuitry 36, receive circuitry38, multiple antennas 40, and user interface circuitry 42. The receivecircuitry 38 receives radio frequency signals bearing information fromone or more base stations 14. A low noise amplifier and a filter (notshown) may co-operate to amplify and remove broadband interference fromthe signal for processing. Downconversion and digitization circuitry(not shown) will then downconvert the filtered, received signal to anintermediate or baseband frequency signal, which is then digitized intoone or more digital streams.

The baseband processor 34 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. The baseband processor 34 is generallyimplemented in one or more digital signal processors (DSPs) andapplication specific integrated circuits (ASICs).

For transmission, the baseband processor 34 receives digitized data,which may represent voice, data, or control information, from thecontrol system 32, which it encodes for transmission. The encoded datais output to the transmit circuitry 36, where it is used by a modulatorto modulate a carrier signal that is at a desired transmit frequency orfrequencies. A power amplifier (not shown) will amplify the modulatedcarrier signal to a level appropriate for transmission, and deliver themodulated carrier signal to the antennas 40 through a matching network(not shown). Various modulation and processing techniques available tothose skilled in the art are used for signal transmission between themobile terminal and the base station.

In OFDM modulation, the transmission band is divided into multiple,orthogonal carrier waves. Each carrier wave is modulated according tothe digital data to be transmitted. Because OFDM divides thetransmission band into multiple carriers, the bandwidth per carrierdecreases and the modulation time per carrier increases. Since themultiple carriers are transmitted in parallel, the transmission rate forthe digital data, or symbols, on any given carrier is lower than when asingle carrier is used.

OFDM modulation utilizes the performance of an Inverse Fast FourierTransform (IFFT) on the information to be transmitted. For demodulation,the performance of a Fast Fourier Transform (FFT) on the received signalrecovers the transmitted information. In practice, the IFFT and FFT areprovided by digital signal processing carrying out an Inverse DiscreteFourier Transform (IDFT) and Discrete Fourier Transform (DFT),respectively. Accordingly, the characterizing feature of OFDM modulationis that orthogonal carrier waves are generated for multiple bands withina transmission channel. The modulated signals are digital signals havinga relatively low transmission rate and capable of staying within theirrespective bands. The individual carrier waves are not modulateddirectly by the digital signals. Instead, all carrier waves aremodulated at once by IFFT processing.

In operation, OFDM is preferably used for at least down-linktransmission from the base stations 14 to the mobile terminals 16. Eachbase station 14 is equipped with “n” transmit antennas 28, and eachmobile terminal 16 is equipped with “m” receive antennas 40. Notably,the respective antennas can be used for reception and transmission usingappropriate duplexers or switches and are so labelled only for clarity.

With reference to FIG. 31, a logical OFDM transmission architecture willbe described. Initially, the base station controller 10 will send datato be transmitted to various mobile terminals 16 to the base station 14.The base station 14 may use the channel quality indicators (CQIs)associated with the mobile terminals to schedule the data fortransmission as well as select appropriate coding and modulation fortransmitting the scheduled data. The CQIs may be directly from themobile terminals 16 or determined at the base station 14 based oninformation provided by the mobile terminals 16. In either case, the CQIfor each mobile terminal 16 is a function of the degree to which thechannel amplitude (or response) varies across the OFDM frequency band.

Scheduled data 44, which is a stream of bits, is scrambled in a mannerreducing the peak-to-average power ratio associated with the data usingdata scrambling logic 46. A cyclic redundancy check (CRC) for thescrambled data is determined and appended to the scrambled data usingCRC adding logic 48. Next, channel coding is performed using channelencoder logic 50 to effectively add redundancy to the data to facilitaterecovery and error correction at the mobile terminal 16. Again, thechannel coding for a particular mobile terminal 16 is based on the CQI.In some implementations, the channel encoder logic 50 uses known Turboencoding techniques. The encoded data is then processed by rate matchinglogic 52 to compensate for the data expansion associated with encoding.

Bit interleaver logic 54 systematically reorders the bits in the encodeddata to minimize the loss of consecutive data bits. The resultant databits are systematically mapped into corresponding symbols depending onthe chosen baseband modulation by mapping logic 56. Preferably,Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Key(QPSK) modulation is used. The degree of modulation is preferably chosenbased on the CQI for the particular mobile terminal. The symbols may besystematically reordered to further bolster the immunity of thetransmitted signal to periodic data loss caused by frequency selectivefading using symbol interleaver logic 58.

At this point, groups of bits have been mapped into symbols representinglocations in an amplitude and phase constellation. When spatialdiversity is desired, blocks of symbols are then processed by space-timeblock code (STC) encoder logic 60, which modifies the symbols in afashion making the transmitted signals more resistant to interferenceand more readily decoded at a mobile terminal 16. The STC encoder logic60 will process the incoming symbols and provide “n” outputscorresponding to the number of transmit antennas 28 for the base station14. The control system 20 and/or baseband processor 22 as describedabove with respect to FIG. 29 will provide a mapping control signal tocontrol STC encoding. At this point, assume the symbols for the “n”outputs are representative of the data to be transmitted and capable ofbeing recovered by the mobile terminal 16.

For the present example, assume the base station 14 has two antennas 28(n=2) and the STC encoder logic 60 provides two output streams ofsymbols. Accordingly, each of the symbol streams output by the STCencoder logic 60 is sent to a corresponding IFFT processor 62,illustrated separately for ease of understanding. Those skilled in theart will recognize that one or more processors may be used to providesuch digital signal processing, alone or in combination with otherprocessing described herein. The IFFT processors 62 will preferablyoperate on the respective symbols to provide an inverse FourierTransform. The output of the IFFT processors 62 provides symbols in thetime domain. The time domain symbols are grouped into frames, which areassociated with a prefix by prefix insertion logic 64. Each of theresultant signals is up-converted in the digital domain to anintermediate frequency and converted to an analog signal via thecorresponding digital up-conversion (DUC) and digital-to-analog (D/A)conversion circuitry 66. The resultant (analog) signals are thensimultaneously modulated at the desired RF frequency, amplified, andtransmitted via the RF circuitry 68 and antennas 28. Notably, pilotsignals known by the intended mobile terminal 16 are scattered among thesub-carriers. The mobile terminal 16, which is discussed in detailbelow, will use the pilot signals for channel estimation.

Reference is now made to FIG. 32 to illustrate reception of thetransmitted signals by a mobile terminal 16. Upon arrival of thetransmitted signals at each of the antennas 40 of the mobile terminal16, the respective signals are demodulated and amplified bycorresponding RF circuitry 70. For the sake of conciseness and clarity,only one of the two receive paths is described and illustrated indetail. Analog-to-digital (A/D) converter and down-conversion circuitry72 digitizes and downconverts the analog signal for digital processing.The resultant digitized signal may be used by automatic gain controlcircuitry (AGC) 74 to control the gain of the amplifiers in the RFcircuitry 70 based on the received signal level.

Initially, the digitized signal is provided to synchronization logic 76,which includes coarse synchronization logic 78, which buffers severalOFDM symbols and calculates an auto-correlation between the twosuccessive OFDM symbols. A resultant time index corresponding to themaximum of the correlation result determines a fine synchronizationsearch window, which is used by fine synchronization logic 80 todetermine a precise framing starting position based on the headers. Theoutput of the fine synchronization logic 80 facilitates frameacquisition by frame alignment logic 84. Proper framing alignment isimportant so that subsequent FFT processing provides an accurateconversion from the time domain to the frequency domain. The finesynchronization algorithm is based on the correlation between thereceived pilot signals carried by the headers and a local copy of theknown pilot data. Once frame alignment acquisition occurs, the prefix ofthe OFDM symbol is removed with prefix removal logic 86 and resultantsamples are sent to frequency offset correction logic 88, whichcompensates for the system frequency offset caused by the unmatchedlocal oscillators in the transmitter and the receiver. Preferably, thesynchronization logic 76 includes frequency offset and clock estimationlogic 82, which is based on the headers to help estimate such effects onthe transmitted signal and provide those estimations to the correctionlogic 88 to properly process OFDM symbols.

At this point, the OFDM symbols in the time domain are ready forconversion to the frequency domain using FFT processing logic 90. Theresults are frequency domain symbols, which are sent to processing logic92. The processing logic 92 extracts the scattered pilot signal usingscattered pilot extraction logic 94, determines a channel estimate basedon the extracted pilot signal using channel estimation logic 96, andprovides channel responses for all sub-carriers using channelreconstruction logic 98. In order to determine a channel response foreach of the sub-carriers, the pilot signal is essentially multiple pilotsymbols that are scattered among the data symbols throughout the OFDMsub-carriers in a known pattern in both time and frequency. Examples ofscattering of pilot symbols among available sub-carriers over a giventime and frequency plot in an OFDM environment are found in PCT PatentApplication No. PCT/CA2005/000387 filed Mar. 15, 2005 assigned to thesame assignee of the present application. Continuing with FIG. 32, theprocessing logic compares the received pilot symbols with the pilotsymbols that are expected in certain sub-carriers at certain times todetermine a channel response for the sub-carriers in which pilot symbolswere transmitted. The results are interpolated to estimate a channelresponse for most, if not all, of the remaining sub-carriers for whichpilot symbols were not provided. The actual and interpolated channelresponses are used to estimate an overall channel response, whichincludes the channel responses for most, if not all, of the sub-carriersin the OFDM channel.

The frequency domain symbols and channel reconstruction information,which are derived from the channel responses for each receive path areprovided to an STC decoder 100, which provides STC decoding on bothreceived paths to recover the transmitted symbols. The channelreconstruction information provides equalization information to the STCdecoder 100 sufficient to remove the effects of the transmission channelwhen processing the respective frequency domain symbols

The recovered symbols are placed back in order using symbolde-interleaver logic 102, which corresponds to the symbol interleaverlogic 58 of the transmitter. The deinterleaved symbols are thendemodulated or de-mapped to a corresponding bitstream using de-mappinglogic 104. The bits are then de-interleaved using bit de-interleaverlogic 106, which corresponds to the bit interleaver logic 54 of thetransmitter architecture. The de-interleaved bits are then processed byrate de-matching logic 108 and presented to channel decoder logic 110 torecover the initially scrambled data and the CRC checksum. Accordingly,CRC logic 112 removes the CRC checksum, checks the scrambled data intraditional fashion, and provides it to the de-scrambling logic 114 forde-scrambling using the known base station de-scrambling code to recoverthe originally transmitted data 116.

In parallel to recovering the data 116, a CQI, or at least informationsufficient to create a CQI at the base station 14, is determined andtransmitted to the base station 14. As noted above, the CQI may be afunction of the carrier-to-interference ratio (CR), as well as thedegree to which the channel response varies across the varioussub-carriers in the OFDM frequency band. The channel gain for eachsub-carrier in the OFDM frequency band being used to transmitinformation is compared relative to one another to determine the degreeto which the channel gain varies across the OFDM frequency band.Although numerous techniques are available to measure the degree ofvariation, one technique is to calculate the standard deviation of thechannel gain for each sub-carrier throughout the OFDM frequency bandbeing used to transmit data.

FIGS. 28 to 32 each provide a specific example of a communication systemor elements of a communication system that could be used to implementembodiments of the invention. It is to be understood that embodiments ofthe invention can be implemented with communications systems havingarchitectures that are different than the specific example, but thatoperate in a manner consistent with the implementation of theembodiments as described herein.

For multi-hop implementations such as described previously, each relaynode will include some transmitting functionality and some receivingfunctionality. For example, a relay station may include components ofthe example OFDM transmitter architecture and the example OFDM receiverarchitecture.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

The invention claimed is:
 1. A method comprising: measuring, at a relaystation, strengths of a plurality of preambles in use in an orthogonalfrequency division multiplexed (OFDM) network, wherein the relay stationis in communication with a base station of the OFDM network and servesat least one mobile station in the OFDM network; generating, at therelay station, a list reporting a preamble index for each of theplurality of preambles, wherein the list identifies each of the preambleindexes whose strength measured by the relay station are higher or lowerthan a pre-defined threshold; and selecting a preamble to transmit basedon the measured strengths of the preambles.
 2. The method of claim 1wherein measuring strengths of a plurality of preambles in use in thesystem is performed during initial network entry.
 3. The method of claim1 wherein selecting a preamble to transmit based on the measuredstrengths of the preambles comprises: selecting at least one preamblehaving a signal strength below a threshold.
 4. The method of claim 3further comprising: signalling the selection of the at least onepreamble back to a serving base station.
 5. A method comprising: a relaystation in communication with a serving base station of the OFDM networkand serves at least one mobile station in the OFDM network, wherein therelay station measures strengths of a plurality of preambles in use inan orthogonal frequency division multiplexed (OFDM) system and feedingat least some of these measurements back to the serving base station andgenerating a list reporting a preamble index for each of the pluralityof preambles, wherein the list identifies each of the preamble indexeswhose strength measured by the relay station are higher or lower than apre-defined threshold; the serving base station selecting a preamble forthe relay to transmit based on the measured strengths of the preamblesand signalling a selected preamble back to the relay.
 6. The method ofclaim 1 wherein signalling to identify preambles is performed usingpreamble indexes.
 7. The method of claim 5 wherein feeding at least someof these measurements back to a serving base station comprises: feedingback the list that includes the plurality of preamble indexes.
 8. Amethod comprising: receiving, at a base station, strength measurementinformation from a mobile station in respect of a plurality of preamblestransmitted by respective relay stations serving the mobile station inan orthogonal frequency division multiplexed (OFDM) network; receiving,at the base station, a list reporting a preamble index for each of theplurality of preambles, wherein the list identifies each of the preambleindexes whose strength measurement information is higher or lower than apre-defined threshold; and allocating resources in a manner resulting inresource re-use based on the strength measurements.
 9. The method ofclaim 8 wherein: allocating resources in a manner resulting in resourcere-use based on the strength measurements comprises allocating resourcesat a first relay station to the mobile station that are also beingallocated at a second relay station whose preamble signal strengthmeasurement was below a defined threshold.
 10. The method of claim 8wherein allocating resources in a manner resulting in resource re-usebased on the strength measurements comprises: if a first mobile stationreports a good signal strength from a first relay station and poorsignal strength from a second relay station, and a second mobile stationreports a good signal strength from the second relay station and poorsignal strength from the first relay station, then in at least someinstances assigning the same or at least partially overlapping resourcesat the first and second relay stations for transmitting to the first andsecond mobile stations with the understanding that this will not resultin interference.
 11. A method for initial access of a relay station (RS)into an orthogonal frequency division multiplexed (OFDM) systemcomprising a base station (BS) and at least one mobile station (MS), themethod comprising: the RS performing downlink (DL) synchronization,including frame synchronization and timing/frequency synchronization,wherein the RS is in communication with the BS and serves the at leastone MS in the OFDM system; the RS performing cell identification andselection; the RS obtaining system parameters from information sent on abroadcast channel by the BS to all receiving stations and decoding thereceived system parameters; the RS generating a list reporting apreamble index for each of the receiving stations, wherein the listidentifies each of the preamble indexes whose strength measured by theRS are higher or lower than a pre-defined threshold; the RS transmittingan initial ranging code; and the RS receiving a response to itstransmitted initial ranging code from the BS.
 12. The method of claim11, further comprising: selecting the initial ranging code from a firstsub-set of ranging codes allocated for use by relay stations in a cellserving the BS, which are different than a second sub-set of rangingcodes allocated for use by mobile stations in the cell serving the BS.13. The method of claim 11, further comprising: selecting the initialranging code from a set of ranging codes allocated for use by relaystations and mobile stations in the cell serving the BS.
 14. The methodof claim 11, further comprising: selecting the initial ranging code froma set of ranging codes allocated for use by relay stations andtransmitting the selected initial ranging code in a time-frequencyregion that is different than a time-frequency region used for MSinitial ranging.
 15. A method for initial access of a relay station (RS)by a mobile station (MS) in an orthogonal frequency division multiplexed(OFDM) system comprising a base station (BS) and at least one RS, themethod comprising: the RS generating a list reporting a preamble indexfor each of a plurality of preambles for use in the OFDM system, whereinthe list identifies each of the preamble indexes whose strength measuredby the RS are higher or lower than a pre-defined threshold, wherein theRS is in communication with the BS and serves the at least one MS in theOFDM system; the RS transmitting a common Sync symbol and preamble toenable downlink (DL) synchronization by the mobile; the RS transmittinginformation on a broadcast channel available to be received and decodedby all who receive the information; the RS detecting an initial rangingcode from the MS; and the RS sending a response to the received initialranging code.
 16. The method of claim 15, wherein the initial rangingcode received by the RS comprises: an initial ranging code selected froma set of RS dedicated initial ranging codes that are specific todifferent RSs respectively in a cell served by the BS.
 17. The method ofclaim 16, wherein information regarding RS dedicated initial rangingcodes is transmitted and readable by all receivers within range of theBS on a BS broadcast channel.
 18. The method of claim 15, whereininitial ranging code received by the RS comprises: an initial rangingcode selected from a set of allocated common initial ranging codes thatare used for the BS and all RSs in a cell served by the BS.
 19. In anorthogonal frequency division multiplexed (OFDM) system comprising abase station (BS), at least one relay station (RS) and a plurality ofmobile station (MSs), a method comprising: an RS receiving a BS preambleand additional information from the BS in a BS downlink (DL)transmission, the additional information including a BS-FCH (BS framecontrol header), BS-MAP (BS-multiplexing access profile), BS-Broadcastinformation, wherein the RS serves at least one of the plurality of MSsin the OFDM system; the RS generating a list reporting a preamble indexfor each of a plurality of preambles for use in the OFDM system, whereinthe list identifies each of the preamble indexes whose strength measuredby the RS are higher or lower than a pre-defined threshold; the RStransmitting in an RS DL transmission an RS preamble and an RS-FCH (RSframe control header), RS-MAP (RS-multiplexing access profile) and theBS-Broadcast information following a duration for receiving theadditional information received from the BS in the BS DL transmission;the at least one RS receiving in an RS UL transmission ranginginformation from any relay stations and MSs with which the at least oneRS is communicating; and the at least one RS transmitting in a BS ULtransmission ranging information from the at least one relay station(RS) and at least some of the plurality of MSs.
 20. The method of claim19 further comprising separating UL transmissions from DL transmissionsusing TDD (time division duplexing).
 21. The method of claim 20 furthercomprising defining TDD frames, each TDD frame comprising a DL sub-frameduring which downlink transmissions for the BS and RSs takes place, anda UL sub-frame during which uplink transmissions to the BS and RSs takesplace, the DL sub-frame and the UL sub-frame being sequentiallytransmitted.
 22. The method of claim 19 further comprising separating ULtransmissions from DL transmissions using FDD (frequency divisionduplexing).
 23. The method of claim 22 further comprising defining FDDframes, each FDD frame comprising a DL frame during which downlinktransmissions for the BS and RSs takes place, and a UL frame duringwhich uplink transmissions to the BS and RSs takes place, the DL frameand the UL frame being simultaneously transmitted using a differentfrequency resource.
 24. The method of claim 19, wherein the duration isthe duration for the RS to receive the additional information from theBS plus a predetermined offset.
 25. The method of claim 19, wherein theduration is a fixed duration.
 26. The method of claim 19, wherein aduration for receiving the additional information is variable induration.